Immunohistochemistry versus microsatellite instability testing for screening colorectal cancer patients at risk for hereditary nonpolyposis colorectal cancer syndrome. Part I. The utility of immunohistochemistry

Clinical significance of combined tumour-infiltrating lymphocytes and microsatellite instability status in colorectal cancer: a systematic review and network meta-analysis

BACKGROUND

Microsatellite instability (MSI) status and tumour-infiltrating lymphocytes (TIL) are established prognostic factors in colorectal cancer. Previous studies evaluating the combination of TIL and MSI status identified distinct colorectal cancer subtypes with unique prognostic associations. However, these studies were often limited by sample size, particularly for MSI-high (MSI-H) tumours, and there is no comprehensive summary of the available evidence. We aimed to review the literature to compare the survival outcomes associated with the subtypes derived from the integrated MSI-TIL classification in patients with colorectal cancer.

METHODS

In this systematic review and network meta-analysis, we searched PubMed, Embase, Scopus, and the Cochrane Library without language restrictions, for articles published between Jan 1, 1990, and March 13, 2024. Patient cohorts comparing different combinations of TIL (high or low) and MSI status (MSI or microsatellite stable [MSS]) in patients with surgically resected colorectal cancer were included. Studies were excluded if they focused on neoadjuvant therapy or on other immune markers such as B cells or macrophages. Methodological quality assessment was done with the Newcastle-Ottawa scale; data appraisal and extraction was done independently by two reviewers. Summary estimates were extracted from published reports. The primary outcomes were overall survival, disease-free survival, and cancer-specific survival. A frequentist network meta-analysis was done to compare hazard ratios (HRs) and 95% CI for each outcome. The MSI-TIL subgroups were prognostically ranked based on P-score, bias, magnitude, and precision of associations with each outcome. The protocol is registered with PROSPERO (CRD42023461108).

FINDINGS

Of 302 studies initially identified, 21 studies (comprising 14 028 patients) were included in the systematic review and 19 (13 029 patients) in the meta-analysis. Nine studies were identified with a low risk of bias and the remaining ten had a moderate risk of bias. The MSI-TIL-high (MSI-TIL-H) subtype exhibited longer overall survival (HR 0·45, 95% CI 0·34-0·61; I2=77·7%), disease-free survival (0·43, 0·32-0·58; I2=61·6%), and cancer-specific survival (0·53, 0·43-0·66; I2=0%), followed by the MSS-TIL-H subtype for overall survival (HR 0·53, 0·41-0·69; I2=77·7%), disease-free survival (0·52, 0·41-0·64; I2=61·6%), and cancer-specific survival (0·55, 0·47-0·64; I2=0%) than did patients with MSS-TIL-low tumours (MSS-TIL-L). Patients with the MSI-TIL-L subtype had similar overall survival (0·88, 0·66-1·18; I2=77·7%) and disease-free survival (0·93, 0·69-1·26; I2=61·6%), but a modestly longer cancer-specific survival (0·72, 0·57-0·90; I2=0%) than did the MSS-TIL-L subtype. Results from the direct and indirect evidence were strongly congruous.

INTERPRETATION

The findings from this network meta-analysis suggest that better survival was only observed among patients with TIL-H colorectal cancer, regardless of MSI or MSS status. The integrated MSI-TIL classification should be further explored as a predictive tool for clinical decision-making in early-stage colorectal cancer.

FUNDING

German Research Council (HO 5117/2-2).

Immunotherapy in MMR-d/MSI-H recurrent/metastatic endometrial cancer

INTRODUCTION

The advent of immunotherapy with immune checkpoint inhibitors (ICIs) has revolutionized the management of mismatch repair deficient (MMR-d)/microsatellite instability-high (MSI-H) endometrial cancer (EC). Initially investigated as monotherapy in phase I-II clinical trials for recurrent disease, immunotherapy demonstrated remarkable activity, yielding overall response rates (ORR) ranging from 27% to 58%. Based on these promising findings, phase III trials have explored the integration of immunotherapy into first-line treatment regimens for advanced/recurrent EC in combination with chemotherapy or other agents such as tyrosine kinase inhibitors (TKIs), resulting in improved ORR, progression-free survival, and overall survival compared to the standard chemotherapy regimen of paclitaxel and carboplatin. As a result, the incorporation of ICIs with standard platinum-based chemotherapy is becoming a new standard of care in MMR-d/MSI-H EC.

AREAS COVERED

This review synthesizes literature from PubMed, Embase databases, and recent congress abstracts on gynecological cancers. It covers MMR-d/MSI-H EC incidence, molecular diagnostics, clinical trial outcomes, predictive biomarkers for ICIs, patient profiles likely to benefit, resistance mechanisms, and the future of immunotherapy in this setting.

EXPERT OPINION

By offering a comprehensive overview, this review delineates the pivotal role of ICIs in the management of MMR-d/MSI-H EC.

The mechanism of RGS5 regulating gastric cancer mismatch repair protein

The incidence and mortality rates of gastric cancer (GC) remain alarmingly high worldwide, imposing a substantial healthcare burden. In this study, we utilized data from The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) databases. A 4-gene prognostic model was developed to predict patient prognosis, and its accuracy was validated across multiple datasets. Patients with a low-risk score exhibited improved prognosis, elevated tumor mutation burden, heightened sensitivity to both immunotherapy and conventional chemotherapy. Notably, our investigation revealed that the key gene RGS5 positively modulates the expression of mismatch repair proteins via c-Myc. Furthermore, co-immunoprecipitation (COIP) assays demonstrated the interaction between RGS5 and c-Myc. Additionally, we confirmed that RGS5 regulates c-Myc through the ubiquitin-proteasome pathway. Moreover, RGS5 was identified as a positive regulator of PD-L1 expression and exhibited a negative correlation with the majority of immune cells. These findings underscore the potential of RGS5 as a novel biomarker and therapeutic target in the context of GC.

Microsatellite instability in mismatch repair proficient colorectal cancer: clinical features and underlying molecular mechanisms

BACKGROUND

Both defects in mismatch repair (dMMR) and high microsatellite instability (MSI-H) have been recognised as crucial biomarkers that guide treatment strategies and disease management in colorectal cancer (CRC). As MMR and MSI tests are being widely conducted, an increasing number of MSI-H tumours have been identified in CRCs with mismatch repair proficiency (pMMR). The objective of this study was to assess the clinical features of patients with pMMR/MSI-H CRC and elucidate the underlying molecular mechanism in these cases.

METHODS

From January 2015 to December 2018, 1684 cases of pMMR and 401 dMMR CRCs were enrolled. Of those patients, 93 pMMR/MSI-H were identified. The clinical phenotypes and prognosis were analysed. Frozen and paraffin-embedded tissue were available in 35 patients with pMMR/MSI-H, for which comprehensive genomic and transcriptomic analyses were performed.

FINDINGS

In comparison to pMMR/MSS CRCs, pMMR/MSI-H CRCs exhibited significantly less tumour progression and better long-term prognosis. The pMMR/MSI-H cohorts displayed a higher presence of CD8+ T cells and NK cells when compared to the pMMR/MSS group. Mutational signature analysis revealed that nearly all samples exhibited deficiencies in MMR genes, and we also identified deleterious mutations in MSH3-K383fs.

INTERPRETATION

This study revealed pMMR/MSI-H CRC as a distinct subgroup within CRC, which manifests diverse clinicopathological features and long-term prognostic outcomes. Distinct features in the tumour immune-microenvironment were observed in pMMR/MSI-H CRCs. Pathogenic deleterious mutations in MSH3-K383fs were frequently detected, suggesting another potential biomarker for identifying MSI-H.

FUNDING

This work was supported by the Science and Technology Commission of Shanghai Municipality (20DZ1100101).

Null Mismatch Repair Proteins Expression Reveals the Temporal Molecular Events in Lynch Syndrome-Related Cancers

The immunohistochemical assessment of mismatch repair (MMR) proteins represents a pivotal screening tool for identifying Lynch syndrome (LS)-related cancers, as the loss of their expression often indicates MMR dysfunction associated with genetic or epigenetic alterations. Frequently, LS-related colorectal cancers present germline pathogenic variants in the MLH1 or MSH2 genes, which result in the simultaneous immunohistochemical loss of MLH1 and PMS2 or MSH2 and MSH6 proteins expression, respectively. Less commonly observed is the single involvement of the MSH6 or PMS2 proteins expression, indicative of the presence of germline pathogenic variants in the corresponding genes. Extremely rarely reported are the null immunohistochemistry phenotypes represented by the complete loss of expression of all MMR proteins. The molecular mechanisms contributing to the raising of this latter uncommon immunohistochemical phenotype are derived from the combination of pathogenic germline variants in MMR genes with the somatic hypermethylation of the MLH1 gene promoter. This study focuses on elucidating the molecular cascade leading to the development of the null immunohistochemical phenotype, providing valuable insights into understanding the sequential molecular events driving the LS-associated tumorigenesis, which may have pivotal implications in the clinical management of patients with LS-related cancers.

Clinical features and oncological outcomes of bladder cancer microsatellite instability

OBJECTIVES

Excellent anticancer effect for solid tumors with microsatellite instability (MSI)-high by anti-PD-1 antibody has been reported. In this study, we investigated the clinical impact of MSI status in bladder cancer.

METHODS

This study included 205 Japanese patients who underwent transurethral resection for bladder cancer between 2005 and 2021. The prevalence rates of microsatellite stable (MSS), MSI-low (MSI-L), and MSI-high (MSI-H) were determined using molecular testing. We examined the association of MSI status (MSS versus MSI-L/H) with clinicopathological characteristics and oncological outcomes.

RESULTS

MSI-L/H tumors were associated with higher T-category in non-muscle invasive bladder cancer (NMIBC). Additionally, MSI-L/H tumors were associated with a higher risk of intravesical recurrence in NMIBC patients treated with intravesical bacillus Calmette-Guérin (BCG) but not with non-BCG therapy.

CONCLUSIONS

This study suggested that the MSI status might serve as a predictive marker for intravesical recurrence after BCG intravesical therapy in NMIBC and highlighted an unmet need for an alternative treatment in patients with MSI-L/H tumors.

MRE11A: a novel negative regulator of human DNA mismatch repair

BACKGROUND

DNA mismatch repair (MMR) is a highly conserved pathway that corrects DNA replication errors, the loss of which is attributed to the development of various types of cancers. Although well characterized, MMR factors remain to be identified. As a 3'-5' exonuclease and endonuclease, meiotic recombination 11 homolog A (MRE11A) is implicated in multiple DNA repair pathways. However, the role of MRE11A in MMR is unclear.

METHODS

Initially, short-term and long-term survival assays were used to measure the cells' sensitivity to N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Meanwhile, the level of apoptosis was also determined by flow cytometry after MNNG treatment. Western blotting and immunofluorescence assays were used to evaluate the DNA damage within one cell cycle after MNNG treatment. Next, a GFP-heteroduplex repair assay and microsatellite stability test were used to measure the MMR activities in cells. To investigate the mechanisms, western blotting, the GFP-heteroduplex repair assay, and chromatin immunoprecipitation were used.

RESULTS

We show that knockdown of MRE11A increased the sensitivity of HeLa cells to MNNG treatment, as well as the MNNG-induced DNA damage and apoptosis, implying a potential role of MRE11 in MMR. Moreover, we found that MRE11A was largely recruited to chromatin and negatively regulated the DNA damage signals within the first cell cycle after MNNG treatment. We also showed that knockdown of MRE11A increased, while overexpressing MRE11A decreased, MMR activity in HeLa cells, suggesting that MRE11A negatively regulates MMR activity. Furthermore, we show that recruitment of MRE11A to chromatin requires MLH1 and that MRE11A competes with PMS2 for binding to MLH1. This decreases PMS2 levels in whole cells and on chromatin, and consequently comprises MMR activity.

CONCLUSIONS

Our findings reveal that MRE11A is a negative regulator of human MMR.

Body size and risk of colorectal cancer molecular defined subtypes and pathways: Mendelian randomization analyses

BACKGROUND

Obesity has been positively associated with most molecular subtypes of colorectal cancer (CRC); however, the magnitude and the causality of these associations is uncertain.

METHODS

We used Mendelian randomization (MR) to examine potential causal relationships between body size traits (body mass index [BMI], waist circumference, and body fat percentage) with risks of Jass classification types and individual subtypes of CRC (microsatellite instability [MSI] status, CpG island methylator phenotype [CIMP] status, BRAF and KRAS mutations). Summary data on tumour markers were obtained from two genetic consortia (CCFR, GECCO).

FINDINGS

A 1-standard deviation (SD:5.1 kg/m2) increment in BMI levels was found to increase risks of Jass type 1MSI-high,CIMP-high,BRAF-mutated,KRAS-wildtype (odds ratio [OR]: 2.14, 95% confidence interval [CI]: 1.46, 3.13; p-value = 9 × 10-5) and Jass type 2non-MSI-high,CIMP-high,BRAF-mutated,KRAS-wildtype CRC (OR: 2.20, 95% CI: 1.26, 3.86; p-value = 0.005). The magnitude of these associations was stronger compared with Jass type 4non-MSI-high,CIMP-low/negative,BRAF-wildtype,KRAS-wildtype CRC (p-differences: 0.03 and 0.04, respectively). A 1-SD (SD:13.4 cm) increment in waist circumference increased risk of Jass type 3non-MSI-high,CIMP-low/negative,BRAF-wildtype,KRAS-mutated (OR 1.73, 95% CI: 1.34, 2.25; p-value = 9 × 10-5) that was stronger compared with Jass type 4 CRC (p-difference: 0.03). A higher body fat percentage (SD:8.5%) increased risk of Jass type 1 CRC (OR: 2.59, 95% CI: 1.49, 4.48; p-value = 0.001), which was greater than Jass type 4 CRC (p-difference: 0.03).

INTERPRETATION

Body size was more strongly linked to the serrated (Jass types 1 and 2) and alternate (Jass type 3) pathways of colorectal carcinogenesis in comparison to the traditional pathway (Jass type 4).

FUNDING

Cancer Research UK, National Institute for Health Research, Medical Research Council, National Institutes of Health, National Cancer Institute, American Institute for Cancer Research, Brigham and Women's Hospital, Prevent Cancer Foundation, Victorian Cancer Agency, Swedish Research Council, Swedish Cancer Society, Region Västerbotten, Knut and Alice Wallenberg Foundation, Lion's Cancer Research Foundation, Insamlingsstiftelsen, Umeå University. Full funding details are provided in acknowledgements.

Validation of a one-step genomics-based molecular classifier for endometrial carcinoma in a large Chinese population

OBJECTIVE

The aim of this study is to delineate the molecular classification features within Chinese endometrial cancer (EC) patients and to evaluate the concurrence between two widely employed methods for diagnosing EC molecular subtypes.

METHODS

This retrospective observational cohort study encompassed 479 cases of EC for analysis. Utilizing next-generation sequencing (NGS) panels targeting POLE, TP53, and microsatellite instability (MSI) status, four subtypes [POLE ultramutated (POLE mut), MMR-deficient (MMRd), p53 abnormal (p53abn), and no specific molecular profile (NSMP)] were classified. Immunohistochemistry (IHC) was employed to ascertain the expression of p53 and MMR proteins.

RESULTS

Among the 479 patients, the distribution of EC subtypes was as follows: 28 (5.85%) POLE mut, 67 (13.99%) MMRd, 60 (12.53%) p53abn, and 324 (67.64%) NSMP. When compared to published findings on EC subtypes in the Caucasian population, our real-world data on Chinese ECs revealed a notably higher proportion of NSMP/CNL (copy number low). The evaluation of MSI/MMR status through NGS-based and IHC-based methods displayed substantial concordance (Kappa = 0.91). Slight discordance between the two techniques in identifying p53 abnormalities (Kappa = 0.83) might stem from TP53 truncating mutations, cytoplasmic p53 expression, null TP53 mutants, and well-documented challenges in interpreting p53 IHC.

CONCLUSIONS

Chinese ECs exhibit distinctive molecular attributes. For accurate molecular subtyping of Chinese ECs, additional molecular markers that align with the Chinese population's characteristics should be incorporated into existing classifiers. The study's outcomes underscore a strong agreement between NGS and IHC in TP53/p53 detection and MSI assessment.

Evaluation of mismatch-repair and microsatellite-instability status in a Chinese colorectal cancer Cohort

BACKGROUND

Immunohistochemistry (IHC) and traditional polymerase chain reaction (PCR) are the methods of choice in clinical practice to identify the mismatch repair (MMR) and microsatellite instability (MSI) status in colorectal cancer (CRC). In some previous researches, the concordance rate between two methods was different and discordance existed in about 1 %-9.7 %.

METHODS

We retrospectively reviewed 406 patients received surgical CRC resections and tests of both MMR IHC and MSI PCR from January 2019 to April 2022 in Shanghai Changzheng Hospital. The incidence of deficient mismatch repair (dMMR) or microsatellite instability-high (MSI-H) CRCs, the concordance rate between two methods, and the reasons for discordant results were evaluated with clinicopathological data, immunochemical staining, whole-exome sequencing, and MLH1 methylation analysis.

RESULTS

Among 406 patients, the incidence of MSI-H CRCs was 7.88 %. Nearly a quarter of the cases under reexamination of IHC was initial misinterpreted. Besides, the concordance rate between MMR IHC and MSI PCR was 99.26 % (401 of 404) and the Kappa value was 0.945 (p < 0.001). Finally, some somatic variants of MMR and POLE genes which may explain the discordance were identified.

CONCLUSION

The incidence rate of MSI-H in Chinese patients with CRC might be relatively low owing to tumor location. Although MSI and IHC analyses are highly concordant, both MMR IHC and MSI PCR tests should be simultaneously performed and MMR IHC should be interpreted by experienced pathologists. In the future, further studies on discordant results should be carried out to improve the personalized management of CRC.

Characterization of mismatch-repair/microsatellite instability-discordant endometrial cancers

BACKGROUND

Mismatch-repair (MMR)/microsatellite instability (MSI) status has therapeutic implications in endometrial cancer (EC). The authors evaluated the concordance of testing and factors contributing to MMR expression heterogeneity.

METHODS

Six hundred sixty-six ECs were characterized using immunohistochemistry (IHC), MSI testing, and mut-L homolog 1 (MLH1) methylation. Select samples underwent whole-transcriptome analysis and next-generation sequencing. MMR expression of metastatic/recurrent sites was evaluated.

RESULTS

MSI testing identified 27.3% of cases as MSI-high (n = 182), MMR IHC identified 25.1% cases as MMR-deficient (n = 167), and 3.8% of cases (n = 25) demonstrated discordant results. A review of IHC staining explained discordant results in 18 cases, revealing subclonal loss of MLH1/Pms 1 homolog 2 (PMS2) (n = 10) and heterogeneous MMR IHC (mut-S homolog 6 [MSH6], n = 7; MLH1/PMS2, n = 1). MSH6-associated Lynch syndrome was diagnosed in three of six cases with heterogeneous expression. Subclonal or heterogeneous cases had a 38.9% recurrence rate (compared with 16.7% in complete MMR-deficient cases and 9% in MMR-proficient cases) and had abnormal MMR IHC results in all metastatic recurrent sites (n = 7). Tumors with subclonal MLH1/PMS2 demonstrated 74 differentially expressed genes (determined using digital spatial transcriptomics) when stratified by MLH1 expression, including many associated with epithelial-mesenchymal transition.

CONCLUSIONS

Subclonal/heterogeneous MMR IHC cases showed epigenetic loss in 66.7%, germline mutations in 16.7%, and somatic mutations in 16.7%. MMR IHC reported as intact/deficient missed 21% of cases of Lynch syndrome. EC with subclonal/heterogeneous MMR expression demonstrated a high recurrence rate, and metastatic/recurrent sites were MMR-deficient. Transcriptional analysis indicated an increased risk for migration/metastasis, suggesting that clonal MMR deficiency may be a driver for tumor aggressiveness. Reporting MMR IHC only as intact/deficient, without reporting subclonal and heterogeneous staining, misses opportunities for biomarker-directed therapy.

PLAIN LANGUAGE SUMMARY

Endometrial cancer is the most common gynecologic cancer, and 20%-40% of tumors have a defect in DNA proofreading known as mismatch-repair (MMR) deficiency. These results can be used to guide therapy. Tests for this defect can yield differing results, revealing heterogeneous (mixed) proofreading capabilities. Tumors with discordant testing results and mixed MMR findings can have germline or somatic defects in MMR genes. Cells with deficient DNA proofreading in tumors with mixed MMR findings have DNA expression profiles linked to more aggressive characteristics and cancer spread. These MMR-deficient cells may drive tumor behavior and the risk of spreading cancer.

Attack of the clones: Unveiling subclonal/heterogenous mismatch repair/microsatellite instability status in endometrial cancer

Any time there are two or more tests for a given analyte, there will be some degree of disagreement between them. This editorial contextualizes the recent findings by Riedinger and colleagues regarding discordant mismatch repair and microsatellite instability testing in endometrial cancer.

An Innovative and Accurate Next-Generation Sequencing-Based Microsatellite Instability Detection Method for Colorectal and Endometrial Tumors

The detection of microsatellite instability (MSI) and mismatch repair (MMR) deficiency has become mandatory for most tumors in recent years, owing to the development of immune checkpoint inhibitors as a highly effective therapy for MMR deficiency/MSI tumors. The timely and efficient detection of MSI is valuable, and new methods are increasingly being developed. To date, MMR assessment has been performed using immunohistochemistry of the 4 MMR proteins and/or microsatellite stability/MSI using PCR, mostly using the pentaplex panel. The implementation of next-generation sequencing (NGS) for MSI analysis would improve the effectiveness at a lower cost and in less time. This study describes the development of 8 new microsatellites combined with a classification algorithm, termed "Octaplex CaBio-MSID" (for Cancérologie Biologique MSI Detection tool), to assess MSI using NGS. A series of 303 colorectal cancer and 88 endometrial cancer samples were assessed via MSI testing using NGS using the Octaplex CaBio-MSID algorithm. The sensitivity and specificity of Octaplex CaBio-MSID were 98.4% and 98.4% for colorectal cancers, and 89.3% and 100% for endometrial cancers, respectively. This new NGS-based MSI detection method outperforms previously published methods (ie, Idylla [Biocartis], OncoMate MSI Dx [Promega], and Foundation One CDx [Roche Foundation Medicine]). Although highly efficient, Octaplex CaBio-MSID requires validation in a larger independent series of different tumor types.

Deficient mismatch repair/microsatellite unstable colorectal cancer: therapeutic advances and questions

The microsatellite instability (MSI) phenotype is related to a deficiency of the DNA mismatch repair (dMMR) system and is observed in 5% of metastatic colorectal cancers (mCRCs). MSI/dMMR phenotype testing should be routine for all CRCs regardless of stage. Two complementary techniques with a high concordance (90-97%) allow us to determine the MSI/dMMR status of a tumor: immunohistochemistry and polymerase chain reaction. Since 2020 and the results of the phase III KEYNOTE 177 trial, pembrolizumab [anti-programmed cell death protein 1 (PD1)] is the new standard of care in first-line MSI/dMMR mCRC. To date, no combination of chemtotherapy ± targeted therapy with immune checkpoint inhibitors (ICIs) has been validated in the management of MSI/dMMR mCRC, and it is not known whether this combination would be beneficial. It is also unclear whether dual therapy with two ICIs is more effective than monotherapy. Several phase III trials are ongoing to answer these questions. Despite a high response rate and long-term benefit of a first line by anti-PD1, 30-50% of patients with MSI/dMMR mCRC experience an early or secondary progression. There are currently no validated predictive biomarkers of anti-PD1 ± anti-cytotoxic T lymphocyte antigen-4 resistance in patients with MSI/dMMR mCRC. In case of early progression on ICIs, the first two questions to consider are the possibility of pseudoprogression and the correct diagnosis of MSI/dMMR status. To date, there are no data on the use of adjuvant ICIs for MSI/dMMR resected colon cancers. By contrast, data are accumulating regarding the efficacy of neoadjuvant ICIs, with at least two-thirds of patients in the different trials in pathological complete response, making it possible to envisage 'Watch and wait' strategies in future.

DNA repair deficiency and the immune microenvironment: A pathways perspective

Timely and accurate repair of DNA damage is required for genomic stability, but DNA repair pathways are often lost or altered in tumors. In addition to directly impacting tumor cell response to DNA damage, DNA repair deficiency can also alter the immune microenvironment via changes in innate and adaptive immune signaling. In some settings, these changes can lead to increased sensitivity to immune checkpoint inhibitors (ICIs). In this review, we discuss the impact of specific DNA repair pathway dysfunction on immune contexture and ICI response in solid tumors.

Exploring the connection between microsatellite instability and inflammatory indicators in cancers

Aim: This study aimed to investigate the association between microsatellite instability (MSI) status and inflammatory indicators in patients with cancer. Patients & methods: A total of 204 patients with various cancer diagnoses, including 102 with MSI-high (MSI-H) and 102 with microsatellite stable tumors, were enrolled. Neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), lymphocyte-to-monocyte ratio (LMR), C-reactive protein (CRP)-to-albumin ratio and systemic immune-inflammation index were evaluated. Results: In microsatellite stable patients, NLR, LMR, PLR and systemic immune-inflammation index were significantly linked to worse survival in univariate analysis, and having a LMR ≤2.6 negatively affected survival in multivariate analysis, although these indicators did not affect the survival of MSI-H patients. Conclusion: The impact of chronic inflammation on survival varies with MSI status. Further research is needed for targeted therapies in different tumors.

Screening and Management of Lynch Syndrome: The Chinese Experience

Lynch syndrome (LS), caused by germline mutations in the mismatch repair genes, is the most common hereditary colorectal cancer. While LS is also associated with various cancers, early detection of the proband is meaningful for tumor prevention, treatment, and familial management. It has been a dramatic shift on the screening approaches for LS. As the rapid development of the molecular biological methods, a comprehensive understanding of the LS screening strategies will help to improve the clinical care for this systematic disease. The current screening strategies have been well validated but mainly by evidence derived from western population, lacking consideration of the ethnic heterogeneity, which hampers the universality and clinical application in China. Hence, this review will focus on the Chinese experience in LS screening, aiming to help better understand the ethnic diversity and further optimize the screening strategies.

Unraveling Resistance to Immunotherapy in MSI-High Colorectal Cancer

Colorectal cancer (CRC) is the third most common cancer and the second leading cause of cancer-related deaths. Incidences of early CRC cases are increasing annually in high-income countries, necessitating effective treatment strategies. Immune checkpoint inhibitors (ICIs) have shown significant clinical efficacy in various cancers, including CRC. However, their effectiveness in CRC is limited to patients with mismatch-repair-deficient (dMMR)/microsatellite instability high (MSI-H) disease, which accounts for about 15% of all localized CRC cases and only 3% to 5% of metastatic CRC cases. However, the varied response among patients, with some showing resistance or primary tumor progression, highlights the need for a deeper understanding of the underlying mechanisms. Elements involved in shaping the response to ICIs, such as tumor microenvironment, immune cells, genetic changes, and the influence of gut microbiota, are not fully understood thus far. This review aims to explore potential resistance or immune-evasion mechanisms to ICIs in dMMR/MSI-H CRC and the cell types involved, as well as possible pitfalls in the diagnosis of this particular subtype.

Both MLH1 deficiency and BRAFV600E mutation are a unique characteristic of colorectal medullary carcinoma: An observational study

Although immunohistochemistry (IHC) for mismatch repair (MMR) proteins (MMR IHC) is used to identify DNA MMR status, universal screening of all patients with colorectal cancer (CRC) using a combination of both MMR IHC and genetic testing for the BRAFV600E mutation is limited in Japan. This study aimed to better understand the histopathological characteristics of CRCs, which exhibit both deficient mismatch repair (dMMR) and BRAFV600E mutation. MMR IHC of formalin-fixed paraffin-embedded tissues from tumor areas obtained from 651 patients with CRC who underwent surgical resection at Hamamatsu University Hospital (Hamamatsu, Japan) between August 2016 and March 2022 were used to evaluate MMR status, which was determined by staining for the expression of 4 MMR proteins (MLH1, MSH2, PMS2, and MSH6). All dMMR tumors were additionally evaluated for BRAFV600 mutation status via Sanger sequencing. Patient clinical characteristics (age, sex, tumor location, size, and tumor pathology) were then classified using their dMMR and BRAFV600 mutation statuses. Among the 651 patients with CRC, 58 carried tumors with dMMR, of which 52 were deficiency in MLH1 (dMLH1). Interestingly, all 16 medullary carcinomas that were analyzed showed characteristics corresponding to the presence of both dMLH1 and BRAFV600E mutation (P = .01). These results suggest that colorectal medullary carcinomas can be diagnosed based on their unique characteristics of harboring the BRAFV600E mutation and exhibiting dMLH1 expression.

Mismatch Repair Deficiency in Biliary Tract Cancer: Prognostic Implications and Correlation with Histology

INTRODUCTION

Mismatch repair (MMR) deficiency represents a biomarker and therapeutic target in various neoplasms, but its role in biliary tract cancers (BTCs) remains misunderstood.

METHODS

MMR status was retrospectively assessed using immunohistochemistry in 163-BTCs patients. We identified MMR proficiency (pMMR)/deficiency (dMMR) according to the loss of MMR proteins (MLH1, PMS2, MSH2, MSH6). The primary objective of the study was to assess the incidence of dMMR in BTCs; the secondary purpose was to explore its association with prognosis and clinical features.

RESULTS

dMMR was recorded in 9 patients, and it was strongly associated with mucinous histology (p < 0.01). Regarding the prognostic effect, in 122-radically resected patients, disease-free survival (DFS) resulted significantly shorter in dMMR patients compared to pMMR patients (10.7 vs. 31.3 months, p = 0.025) and so did nodal status (48.2 vs. 15.3 months in N0 vs. N+) (p < 0.01). Moreover, dMMR confirmed its prognostic role in terms of DFS at multivariate analysis (p = 0.03), together with nodal status (p = 0.01), and resection margin (p = 0.03). In 103 M+ patients (encompassing 41 metastatic de novo and 62 recurred after surgery patients) there were not differences between dMMR and pMMR regarding survival analyses.

CONCLUSIONS

dMMR status is strongly correlated with mucinous histology and represents an independent prognostic factor in terms of disease relapse in patients with resected BTC.

IMPLICATIONS FOR PRACTICE

MMR may play an independent role in promoting an aggressive behaviour in patients with radically resected BTC. These results could be useful in improving the selection of patients after resection and, above all, should justify the evaluation of MMR status as a therapeutic target in BTC, especially in patients with atypical histology.

Discordant Staining Patterns and Microsatellite Results in Tumors of MSH6 Pathogenic Variant Carriers

Diagnosis of Lynch syndrome (LS) caused by a pathogenic germline MSH6 variant may be complicated by discordant immunohistochemistry (IHC) and/or by a microsatellite stable (MSS) phenotype. This study aimed to identify the various causes of the discordant phenotypes of colorectal cancer (CRC) and endometrial cancer (EC) in MSH6-associated LS. Data were collected from Dutch family cancer clinics. Carriers of a (likely) pathogenic MSH6 variant diagnosed with CRC or EC were categorized based on an microsatellite instability (MSI)/IHC test outcome that might fail to result in a diagnosis of LS (eg, retained staining of all 4 mismatch repair proteins, with or without an MSS phenotype, and other staining patterns). When tumor tissue was available, MSI and/or IHC were repeated. Next-generation sequencing (NGS) was performed in cases with discordant staining patterns. Data were obtained from 360 families with 1763 (obligate) carriers. MSH6 variant carriers with CRC or EC (n = 590) were included, consisting of 418 CRCs and 232 ECs. Discordant staining was reported in 77 cases (36% of MSI/IHC results). Twelve patients gave informed consent for further analysis of tumor material. Upon revision, 2 out of 3 MSI/IHC cases were found to be concordant with the MSH6 variant, and NGS showed that 4 discordant IHC results were sporadic rather than LS-associated tumors. In 1 case, somatic events explained the discordant phenotype. The use of reflex IHC mismatch repair testing, the current standard in most Western countries, may lead to the misdiagnosis of germline MSH6 variant carriers. The pathologist should point out that further diagnostics for inheritable colon cancer, including LS, should be considered in case of a strong positive family history. Germline DNA analysis of the mismatch repair genes, preferably as part of a larger gene panel, should therefore be considered in potential LS patients.

Efficacy and safety of preoperative immunotherapy alone followed by surgery in the treatment of advanced gastric cancer with MSI-H/dMMR or EBV-positive

BACKGROUND

At present, there is no consensus on whether preoperative immunotherapy (PIT) without chemotherapy followed by surgery could benefit patients with advanced gastric cancer (AGC). Here, we report a six-case series study to describe the safety and efficacy of PIT plus gastrectomy in patients with AGC.

METHODS

This study involved six patients with AGC who received PIT and surgery at our center between January 2019 and July 2021. Demographic characteristics, preoperative gastroscope biopsy pathology, surgical tissue pathology, radicalness of tumor resection, surgical safety, and recovery parameters were reported.

RESULTS

Six patients, including four patients with Epstein-Barr virus (EBV)-positive gastric cancer (GC) and two patients with microsatellite instability-high (MSI-H)/expression deficiency of mismatch repair (dMMR) protein GC, were enrolled in this study. Four patients experienced immunotherapy-related adverse events (irAEs), without severe adverse events (SAEs). Five patients underwent R0 resection, and one patient underwent palliative gastrectomy due to liver and hilar lymph node metastasis. Pathologic responses from the surgical tissue were observed in all patients, including two pathological complete response (pCR). No operative complications or postoperative deaths occurred. Three patients (50%) experienced mild or moderate postoperative complications without severe postoperative complications. All six patients eventually recovered and were discharged.

CONCLUSION

This study indicated that PIT was effective and tolerant in some patients with MSI-H/dMMR and/or EBV-positive AGC. PIT followed by gastrectomy might be an alternative treatment option for these selected patients.

The prognostic significance of microsatellite instability in colorectal cancer: a Swedish multi-center study

PURPOSE

About 10 to 15% of patients with sporadic colorectal cancer display mutations in DNA mismatch repair (MMR) genes shown as microsatellite instability (MSI). Previous reports of colorectal cancer (CRC) indicate a better prognosis for patients with MSI tumors compared to patients with microsatellite stable (MSS) tumors. In this study, our aim was to investigate whether MSI is an independent prognostic factor in CRC.

PATIENTS AND METHODS

Patients with stage I-III colorectal cancer and subject to curative surgery during 2002-2006 in the Swedish low-risk colorectal cancer study group cohort were eligible for inclusion. Deficient MMR (dMMR) status was analyzed by immunohistochemistry (IHC) and/or by MSI testing with polymerase chain reaction (PCR). Prognostic follow-up and treatment data were retrieved from patient records. Statistical analyses to assess MSI-status and prognosis were done using logistic regression and survival analyses using the Kaplan-Meier method and Cox regression hazards models adjusted for age, sex, stage, comorbidity, and tumor location.

RESULTS

In total, 463 patients were included, MSI high tumors were present in 66 patients (14%), and the remaining 397 were MSS/MSI low. Within 6 years, distant recurrences were present in 9.1% and 20.2% (P = 0.049), and death occurred in 25.8% and 31.5% in MSI and MSS patients, respectively. There was no statistically significant difference in overall mortality (HR 0.80, 95% CI 0.46-1.38), relapse-free survival (HR 0.82, 95% CI 0.50-1.36), or cancer-specific mortality (HR 1.60, 95% CI 0.73-3.51).

CONCLUSION

Despite distant metastases being less common in patients with MSI, there was no association between MSI and overall, relapse-free, or cancer-specific survival.

Universal screening for Lynch syndrome in operated colorectal cancer by immunohistochemistry: a cohort of patients in Liaoning province, China

OBJECTIVE

Lynch syndrome (LS) is the most common hereditary colorectal cancer syndrome worldwide. Due to the decreasing family size in Liaoning province. The Bethesda and Amsterdam II criteria have lower sensitivity and specificity and are not suitable for the local population. Immunohistochemistry screening for mutations in DNA mismatch repair (MMR) in newly diagnosed colorectal cancer can improve the detection rate of LS.

METHODS

All newly diagnosed colorectal cancer patients who underwent surgery between January 2018 and June 2020 at Cancer Hospital of China Medical University and Shengjing Hospital of China Medical University from Liaoning China were included retrospectively, and the ratio of universal LS screening by immunohistochemistry, MMR protein deficiency (dMMR) ratio, MLH1 loss, MSH2 loss, MSH6 loss, and PMS2 loss was analyzed. The clinicopathological characteristics of patients with pMMR and dMMR were analyzed.

RESULTS

A total of 7019 colorectal cancer patients underwent surgery and 4802 (68.41%) patients were screened by immunohistochemistry for MMR, 258 (5.37%) cases were reported to have a loss of MMR expression. In the dMMR group, a higher number of patients were under 50 years old, more tumors were located at the right colon, less patients have lymph node metastasis, more tumors were stage II, and histological types of mucinous carcinoma or signet ring carcinoma were more common, compared with the pMMR group. Only 2.71% dMMR patients meet Amsterdam criteria II, 2.71% of patients meet Revised Bethesda guidelines, and 17.83% meet Chinese LS criteria. Twenty-five dMMR patients were confirmed by next-generation sequencing and five families were confirmed as Lynch family.

CONCLUSION

These data imply that universal screening for LS by immunohistochemistry may be effective in Liaoning province.

External quality assessment for the molecular detection of microsatellite instability in China, 2021-2022

BACKGROUND

Microsatellite instability (MSI) analysis of tumors informs Lynch syndrome testing, therapeutic choice, and prognosis. The status of MSI is mainly detected by polymerase chain reaction coupled with capillary electrophoresis. However, there are various assays with different detection loci and the obtained results may vary. The objective of this study was to evaluate the concordance among different assays and the performance among different laboratories.

METHODS

External quality assessment (EQA) for the detection of MSI was performed in 2021 and 2022. Each sample panel consisted of five samples, including microsatellite-stable and MSI tumor tissues. The sample panels were coded at random, and the returned results were compared and scored.

RESULTS

The fully validated sample panels showed appropriate applicability with commercially available assays. There were eight false-negative results in 2021 and five false results (two false-positives and three false-negatives) in 2022. Among the participating laboratories, in 2021, 20 (74.07%) provided completely correct results; in 2022, 38 (92.68%) obtained an optimal score.

CONCLUSION

The molecular detection of MSI in China exhibited an improvement in a 2-year EQA study. Participation in EQA program is an efficient way of assessing the performance of laboratories and improving their ability.

Molecular testing of DNA damage response pathways in prostate cancer patients

PURPOSE OF REVIEW

Personalizing prostate cancer therapy requires germline and tumor molecular tests that predict who will respond to specific treatments and who may not. The review covers molecular testing of DNA damage response pathways, the first biomarker-driven precision target with clinical utility for treatment selection in patients with castration resistant prostate cancer (CRPC).

RECENT FINDINGS

Recurrent somatic and germline variants cause deficiency of the mismatch repair (MMR) or homologous recombination (HR) pathways in about a quarter of CRPC patients. In prospective clinical trials, patients with deleterious variants in the MMR pathway more frequently experience a therapeutic response to immune checkpoint inhibitors (ICI). Similarly, somatic and germline events affecting HR predict response to poly(ADP) ribose polymerase inhibitor (PARPi) therapy. Molecular testing of these pathways currently involves assaying for loss of function variants in individual genes and for the genome-wide consequences of repair deficiency.

SUMMARY

DNA damage response pathways are the first major area of molecular genetic testing in CRPC settings and offer insights into this new paradigm. Our hope is that eventually an arsenal of molecularly-guided therapies will be developed across many pathways to enable precision medicine options for most men with prostate cancer.

Germline Cancer Risk Profiles of Patients With Young-Onset Colorectal Cancer: Findings From a Prospective Universal Germline Testing and Telegenetics Program

BACKGROUND

Colorectal cancer is being increasingly diagnosed in people younger than 50 years. An inheritable cancer predisposition has been reported in 22% of the young-onset cases. Assessment of germline risk is critical for personalized cancer care.

OBJECTIVE

The study aimed to implement universal germline cancer risk assessment and testing and to define the germline cancer risk profiles of patients presenting with young-onset disease.

DESIGN

This is a prospective cohort study.

SETTINGS

This study was conducted at a tertiary-referral academic medical center.

PATIENTS

This study included newly diagnosed patients presenting to surgical clinics between September 2019 and February 2021 who were treated on a standardized care pathway including the universal germline risk assessment.

INTERVENTIONS

Patients received educational material on young-onset disease, genetic testing, and insurance coverage followed by genetic counseling (either remotely by telegenetics or in person). Consenting patients were assessed on a 47-gene common hereditary cancer panel.

MAIN OUTCOME MEASURES

The primary outcome was a proportion of patients with identifiable germline cancer predisposition.

RESULTS

Among 500 patients with colorectal cancer, 185 (37%) were 50 years of age or younger (median: 44). A family history was absent for the majority of patients (123; 67%), and in 15 patients, tumors (8.1%) were deficient in DNA mismatch repair. Germline testing was completed in 130 patients (70%); the remainder were pending (7%), deceased (1%), or declined (22%). Pathogenic germline mutations were identified in 25 of 130 (19%) patients: 12 in mismatch repair genes and 13 in other genes. A variant of uncertain significance was found in 23 (18%) patients. Importantly, a pathogenic germline mutation was identified in 12% of the patients without a family history (versus 32% with; p = 0.015) and in 13% of those with proficient mismatch repair colorectal cancers (versus 71% if deficient; p < 0.001).

LIMITATIONS

The study is limited by its implementation at a single tertiary academic institution.

CONCLUSIONS

One in 5 patients with young-onset disease harbored germline cancer predisposition. This detection rate, coupled with a high level of interest and acceptance from patients and feasibility of implementation, supports universal germline cancer risk assessment in this patient population. See Video Abstract at http://links.lww.com/DCR/B925 .

PERFILES DE RIESGO DE CNCER DE LNEA GERMINAL DE PACIENTES CON CNCER COLORRECTAL DE INICIO JOVEN HALLAZGOS DE UN PROGRAMA UNIVERSAL PROSPECTIVO DE PRUEBAS DE LNEA GERMINAL Y TELEGENTICA

ANTECEDENTES:El cáncer colorrectal se diagnostica cada vez más en personas menores de 50 años. Se ha informado una predisposición hereditaria al cáncer en el 22 % de los casos de aparición temprana. La evaluación del riesgo de la línea germinal es fundamental para la atención personalizada del cáncer.OBJETIVO:Implementar la evaluación y las pruebas universales de riesgo de cáncer de línea germinal, y definir los perfiles de riesgo de cáncer de línea germinal de los pacientes que presentan una enfermedad de aparición temprana.DISEÑO:Un estudio de cohorte prospectivo.AJUSTE:Un centro médico académico de referencia terciaria.PACIENTES:Los pacientes recién diagnosticados que se presentaron en clínicas quirúrgicas entre Septiembre de 2019 y Febrero de 2021 fueron tratados en una vía de atención estandarizada que incluye una evaluación de riesgo de línea germinal universal.INTERVENCIÓN:Los pacientes recibieron material educativo sobre enfermedades de aparición temprana, pruebas genéticas y cobertura de seguro, seguido de asesoramiento genético (ya sea a distancia por telegenética o en persona). Los pacientes que dieron su consentimiento fueron evaluados en un panel de cánceres hereditarios comunes de 47 genes.MEDIDA DE RESULTADO PRINCIPAL:Proporción de pacientes con predisposición identificable al cáncer de línea germinal.RESULTADOS:Entre 500 pacientes con cáncer colorrectal, 185 (37%) tenían 50 años o menos (mediana: 44). No había antecedentes familiares en la mayoría (123, 67%) y 15 tumores (8,1%) eran deficientes en la reparación del desajuste de ácido desoxirribonucleico. La prueba de línea germinal se completó en 130 pacientes (70%); el resto estaban pendientes (7%), fallecidos (1%) o declinados (22%). Se identificaron mutaciones patogénicas de la línea germinal en 25 (de 130, 19%) pacientes: 12 en genes de reparación de errores de emparejamiento y 13 en otros genes. Se encontró una variante de significado incierto en 23 (18%) pacientes. Es importante señalar que se identificó una mutación germinal patogénica en el 12% de los pacientes sin antecedentes familiares (frente al 32% con; p = 0,015) y en el 13% de aquellos con cánceres colorrectales competentes en la reparación de errores de emparejamiento (frente al 71% si eran deficientes; p < 0,001).LIMITACIÓN:Implementado en una sola institución académica terciaria.CONCLUSIÓN:Uno de cada cinco pacientes con enfermedad de inicio joven albergaba predisposición al cáncer de línea germinal. Esta tasa de detección, junto con un alto nivel de interés y aceptación por parte de los pacientes y la viabilidad de la implementación, respaldan la evaluación universal del riesgo de cáncer de línea germinal en esta población de pacientes. Consulte el Video Resumen en http://links.lww.com/DCR/B925 . (Traducción-Dr. Yesenia Rojas-Khalil ).

Germline Variants in MLH1 and ATM Genes in a Young Patient with MSI-H in a Precancerous Colonic Lesion

Lynch syndrome (LS) is an autosomal dominant inherited disorder that primarily predisposes individuals to colorectal and endometrial cancer. It is associated with pathogenic variants in DNA mismatch repair (MMR) genes. In this study, we report the case of a 16-year-old boy who developed a precancerous colonic lesion and had a clinical suspicion of LS. The proband was found to have a somatic MSI-H status. Analysis of the coding sequences and flanking introns of the MLH1 and MSH2 genes by Sanger sequencing led to the identification of the variant of uncertain significance, namely, c.589-9_589-6delGTTT in the MLH1 gene. Further investigation revealed that this variant was likely pathogenetic. Subsequent next-generation sequencing panel analysis revealed the presence of two variants of uncertain significance in the ATM gene. We conclude that the phenotype of our index case is likely the result of a synergistic effect of these identified variants. Future studies will allow us to understand how risk alleles in different colorectal-cancer-prone genes interact with each other to increase an individual's risk of developing cancer.

Real-world clinical outcomes of the combination of anti-PD-1 antibody, trastuzumab, and chemotherapy for HER2-positive gastric/gastroesophageal junction cancer

BACKGROUND

Previous clinical trials indicated the addition of anti-PD-1 antibody remarkably improved the efficacy of trastuzumab and chemotherapy in patients with HER2-positive gastric/gastroesophageal junction (GEJ) cancer. However, no real-world experiences have been reported yet.

METHODS

We retrospectively analyzed 1212 patients with gastric/GEJ cancer treated at Nanjing Drum Tower Hospital between 2019 and 2022. Among 138 patients with HER2-positive gastric/GEJ cancer, 47 patients receiving at least two doses of the combination regimen with anti-PD-1 antibody, trastuzumab, and chemotherapy were recruited in the study population, and 38 out of 47 patients with measurable disease were included in the efficacy population. Progression-free survival (PFS), objective response rate (ORR), disease control rate (DCR), and toxicity profiles were reported.

RESULTS

In the study population, 37 (78.7%) received the study therapy as a first-line treatment. In the efficacy population, the ORR and DCR were 76.3% and 94.7%, respectively. The overall median PFS was 9.1 months (95% confidence interval [CI] 6.3-11.9 months). For the first-line treatment, the mPFS was 10 months, and 7 months for the second-line. Among 14 patients who failed the study treatment, three (21.4%) developed brain metastasis as the first failure site. No significant association was found between PFS and the expression of PD-L1. 22.2% of patients developed grade 3 treatment-related adverse events (TRAEs). No treatment-related grade ≥4 adverse events or deaths occurred.

CONCLUSION

This real-world study validated the combination regimen's high efficacy and good tolerance in patients with HER2-positive gastric/GEJ cancer. An increased incidence of brain metastasis was observed in patients who failed this regimen.

The Importance of Immunohistochemical Heterogeneous Expression of MMR Protein in Patients with Colorectal Cancer in Stage II and III of the Disease

Background and objectives: In patients with colorectal cancer (CRC), heterogeneous expression of Mismatch repair (MMR) proteins can manifest itself in several different forms and is not such a rare phenomenon. Therefore, it is very important to recognize the nuclear expression of MMR proteins of different MMR status in order to avoid false positive or false negative results. The aim of this study was to determine the frequency and distribution of heterogeneous expression of MMR proteins in patients with stages II and III of the disease as well as its association with clinical, demographic and pathological characteristics of CRC in relation to proficient and deficient expression of MMR proteins. Material and Methods: The study included 104 cases of colorectal cancer obtained from surgical colectomy material in stages II and III of the disease. Results: From a total of 104 patients with colorectal cancer, immunohistochemical analysis of the expression of all four MMR proteins showed that heterogeneous expression of MMR proteins (as well as deficient immunoreactivity of tumor cells) was present in 12 cases, while proficient expression of MMR proteins was detected in 80 tumors. Conclusions: Our study showed that the only independent predictors of the loss of MMR protein expression were younger patient age and right-sided anatomical location of the tumor. The study also established the existence of heterogeneous expression of MMR proteins in a non-negligible percentage of CRCs (11.5%), where heterogeneous nuclear expression of MMR proteins was described in several different forms.

DeltaMSI: artificial intelligence-based modeling of microsatellite instability scoring on next-generation sequencing data

BACKGROUND

DNA mismatch repair deficiency (dMMR) testing is crucial for detection of microsatellite unstable (MSI) tumors. MSI is detected by aberrant indel length distributions of microsatellite markers, either by visual inspection of PCR-fragment length profiles or by automated bioinformatic scoring on next-generation sequencing (NGS) data. The former is time-consuming and low-throughput while the latter typically relies on simplified binary scoring of a single parameter of the indel distribution. The purpose of this study was to use machine learning to process the full complexity of indel distributions and integrate it into a robust script for screening of dMMR on small gene panel-based NGS data of clinical tumor samples without paired normal tissue.

METHODS

Scikit-learn was used to train 7 models on normalized read depth data of 36 microsatellite loci in a cohort of 133 MMR proficient (pMMR) and 46 dMMR tumor samples, taking loss of MLH1/MSH2/PMS2/MSH6 protein expression as reference method. After selection of the optimal model and microsatellite panel the two top-performing models per locus (logistic regression and support vector machine) were integrated into a novel script (DeltaMSI) for combined prediction of MSI status on 28 marker loci at sample level. Diagnostic performance of DeltaMSI was compared to that of mSINGS, a widely used script for MSI detection on unpaired tumor samples. The robustness of DeltaMSI was evaluated on 1072 unselected, consecutive solid tumor samples in a real-world setting sequenced using capture chemistry, and 116 solid tumor samples sequenced by amplicon chemistry. Likelihood ratios were used to select result intervals with clinical validity.

RESULTS

DeltaMSI achieved higher robustness at equal diagnostic power (AUC = 0.950; 95% CI 0.910-0.975) as compared to mSINGS (AUC = 0.876; 95% CI 0.823-0.918). Its sensitivity of 90% at 100% specificity indicated its clinical potential for high-throughput MSI screening in all tumor types. Clinical Trial Number/IRB B1172020000040, Ethical Committee, AZ Delta General Hospital.

Patterns of DNA mismatch repair protein expression for primary and recurrent colorectal cancer at an advanced surgical unit: A retrospective audit

AIM

Lynch syndrome is an inherited cancer syndrome associated with an increased lifetime risk of colorectal cancer (CRC) and characterized by germline mutations to one of four DNA mismatch repair (MMR) genes. Immunohistochemical (IHC) testing is used to screen for Lynch syndrome; however, despite routine completion following resection of primary CRC, it is only variably completed following resection of recurrent disease. This may be significant, as MMR protein expression can change from primary to recurrent CRC. The primary aim of this study is to investigate how MMR profiles change from primary to recurrent CRC; the secondary aim is to assess rates of MMR testing of primary and recurrent disease.

METHOD

We conducted a retrospective analysis of patients undergoing surgery for recurrent CRC from 2018-19 at a high-volume institution. MMR profiles were obtained following both primary and recurrent resection of CRC, and MMR protein expression was evaluated from both time points.

RESULTS

A total of 107 patients met the inclusion criteria and IHC results were obtained for both primary and recurrent resections in 85 cases. MMR profiles changed in nine patients (10.6%), with a loss of staining from primary to recurrent disease in six (7.1%) and a gain of staining in three (3.5%). IHC testing was completed following 88.7% of primary and 39.3% of recurrent resections.

CONCLUSION

MMR profiles can change from primary to recurrent CRC and repeat MMR testing for recurrent CRC is completed in only a minority of cases.

Histopathological Predictors of Microsatellite Instability in Colorectal Cancer-a Tertiary Care Center Experience

Microsatellite instability (MSI) has a therapeutic and prognostic implication in colorectal carcinomas (CRCs). It can be detected either by immunohistochemistry (IHC) or molecular studies. In developing countries, a significant proportion of the patients experience financial constraints limiting the utilization of healthcare facilities. We aimed to identify the possible clinicopathological variables which can be used as predictors of microsatellite instability in such patients. CRC cases received for MSI detection by IHC (for 1 and 1/2 years) were included. A panel of four IHC markers (anti-MLH1, anti-PMS2, anti-MSH2, and anti-MSH6) was used. Confirmation by the molecular study was recommended in all the IHC-proven MSI cases. Various clinicopathological parameters were evaluated as predictors of MSI. Microsatellite instability was detected in 40.6% (30/74) cases with MLH1 and PMS2 dual loss in 27% cases, MSH2 and MSH6 dual loss in 6.8%, loss of all four MMR proteins in 2.7%, and isolated PMS2 loss in 4.1%. MSI-H expression was shown by 36.5% cases with only 4.1% cases showing MSI-L expression. The age cut-off value to differentiate both the study groups (MSI vs MSS) was 63 years with a sensitivity of 47.7% and specificity of 86.7%. ROC curve showed an area under the curve of 0.65 (95% CI, 0.515-0.776; p-value = 0.03). On univariate analysis, age < 63 years, colon site, and absence of nodal metastasis were significantly higher in the MSI group. However, on multivariate analysis, only the age < 63 years was found to be significantly higher in the MSI group. Confirmation was molecular study could only be obtained in 12 cases and was completely concordant with MSI detection by IHC. MSI detection can be performed either by IHC or by molecular study. In this study, no histological parameter appeared to be the independent predictor of MSI status. The age < 63 years might predict the microsatellite instability, yet larger studies are needed for its validation. Thus, we recommend that IHC testing should be performed in all CRC cases.

Predicting colorectal cancer microsatellite instability with a self-attention-enabled convolutional neural network

This study develops a method combining a convolutional neural network model, INSIGHT, with a self-attention model, WiseMSI, to predict microsatellite instability (MSI) based on the tiles in colorectal cancer patients from a multicenter Chinese cohort. After INSIGHT differentiates tumor tiles from normal tissue tiles in a whole slide image, features of tumor tiles are extracted with a ResNet model pre-trained on ImageNet. Attention-based pooling is adopted to aggregate tile-level features into slide-level representation. INSIGHT has an area under the curve (AUC) of 0.985 for tumor patch classification. The Spearman correlation coefficient of tumor cell fraction given by expert pathologist and INSIGHT is 0.7909. WiseMSI achieves a specificity of 94.7% (95% confidence interval [CI] 93.7%-95.7%), a sensitivity of 84.7% (95% CI 82.6%-86.9%), and an AUC of 0.954 (95% CI 0.948-0.960). Comparative analysis shows that this method has better performance than the other five classic deep learning methods.

Discordance between germline genetic findings and abnormal tumor immunohistochemistry staining of mismatch repair proteins in individuals with suspected Lynch syndrome

Background and Aims

Tumor immunohistochemical staining (IHC) of DNA mismatch repair (MMR) proteins is often used to guide germline genetic testing and variant classification for patients with suspected Lynch syndrome. This analysis examined the spectrum of germline findings in a cohort of individuals showing abnormal tumor IHC.

Methods

We assessed individuals with reported abnormal IHC findings and referred for testing with a six-gene syndrome-specific panel (n=703). Pathogenic variants (PVs) and variants of uncertain significance (VUS) in MMR genes were designated expected/unexpected relative to IHC results.

Results

The PV positive rate was 23.2% (163/703; 95% confidence interval [CI], 20.1%-26.5%); 8.0% (13/163; 95% CI, 4.3%-13.3%) of PV carriers had a PV in an unexpected MMR gene. Overall, 121 individuals carried VUS in MMR genes expected to be mutated based on IHC results. Based on independent evidence, in 47.1% (57/121; 95% CI, 38.0%-56.4%) of these individuals the VUSs were later reclassified as benign and in 14.0% (17/121; 95% CI, 8.4%-21.5%) of these individuals the VUSs were reclassified as pathogenic.

Conclusions

Among patients with abnormal IHC findings, IHC-guided single-gene genetic testing may miss 8% of individuals with Lynch syndrome. In addition, in patients with VUS identified in MMR genes predicted to be mutated by IHC, extreme caution must be taken when the IHC results are considered in variant classification.

Tumors of the Digestive System: Comprehensive Review of Ancillary Testing and Biomarkers in the Era of Precision Medicine

Immunotherapy has remained at the vanguard of promising cancer therapeutic regimens due to its exceptionally high specificity for tumor cells and potential for significantly improved treatment-associated quality of life compared to other therapeutic approaches such as surgery and chemoradiation. This is especially true in the digestive system, where high rates of mutation give rise to a host of targetable tumor-specific antigens. Many patients, however, do not exhibit measurable improvements under immunotherapy due to intrinsic or acquired resistance, making predictive biomarkers necessary to determine which patients will benefit from this line of treatment. Many of these biomarkers are assessed empirically by pathologists according to nuanced scoring criteria and algorithms. This review serves to inform clinicians and pathologists of extant and promising upcoming biomarkers predictive of immunotherapeutic efficacy among digestive system malignancies and the ancillary testing required for interpretation by pathologists according to tumor site of origin.

Relation between mismatch repair status, chemoresponse, survival and anatomic location in gastroesophageal adenocarcinoma

BACKGROUND

It has recently been reported that mismatch repair (MMR) status and microsatellite instability (MSI) status in gastroesophageal carcinomas predict surgical, chemotherapeutic and immunotherapeutic outcomes; however, there is extensive variability in the reported incidence and clinical implications of MMR/MSI status in gastroesophaegal adenocarcinomas. We characterized a Canadian surgical patient cohort with respect to MMR status, clinicopathologic correlates and anatomic tumour location.

METHODS

We investigated MMR and BRAF V600E status of gastroesophaegal adenocarcinomas in patients who underwent gastrectomy or esophagectomy with extended (D2) lymphadenectomy at a single centre between 2011 and 2019. We correlated patterns of MMR expression in the overall cohort and in anatomic location-defined subgroups with treatment response and overall survival using multivariate analysis.

RESULTS

In all, 226 cases of gastroesophaegal adenocarcinoma (63 esophageal, 98 gastroesophageal junctional and 65 gastric) were included. The MMR-deficient (dMMR) immunophenotype was found in 28 tumours (12.3%) (15 junctional [15.3%], 13 gastric [20.0%] and none of the esophageal). The majority (25 [89%]) of dMMR cases showed MLH1/PMS2 loss without concurrent BRAF V600E mutation. Two MSH2/ MSH6-deficient gastric tumours and 1 MSH6-deficient junctional tumour were detected. The pathologic response to preoperative chemotherapy was comparable in the dMMR and MMR-proficient (pMMR) cohorts. However, dMMR status was associated with significantly longer median overall survival than pMMR status (5.8 yr v. 2.4 yr, hazard ratio [HR] 1.91, 95% confidence interval [CI] 1.06-3.46), particularly in junctional tumours (4.6 yr v. 1.9 yr, HR 2.97, 95% CI 1.27-6.94).

CONCLUSION

Our study shows that MMR status has at least prognostic value, which supports the need for biomarker testing in gastroesophageal adenocarcinomas, including junctional adenocarcinomas. This highlights the clinical significance of determining the MMR status in all adenocarcinomas of the upper gastrointestinal tract. Response to induction chemotherapy, however, was not influenced by MMR status.

Microsatellite instability evaluation of patients with solid tumour: routine practice insight from a large series of Italian referral centre

DNA mismatch repair complex is involved in the maintenance of DNA stability. In the recent years, a plethora of technical approaches for microsatellite instability (MSI) analysis emerged. Here, we review the results of our MSI status evaluation by adopting a customised workflow on microfluidic system obtained in 4 years of diagnostic routine practice. Data from MSI status were retrieved from our institutional archive covering the period from January 2017 to December 2021. Microfluidic analysis was carried out on microfluidic platform. Results were inspected with a proprietary software. Overall, microsatellite stability (MSS) and MSI-high (MSI-H) profile was detected in n=423/458 (92.36%) and n=35/458 (7.64%) patients with metastatic CRC (mCRC), respectively. In addition, n=78/86 (90.70%) and n=8/86 (9.30%) patients without CRC showed an MSS and MSI-H profile. This review highlights the suitability of microfluidic approach in patients with cancer for MSI testing.

Evaluating Multiple Next-Generation Sequencing-Derived Tumor Features to Accurately Predict DNA Mismatch Repair Status

Identifying tumor DNA mismatch repair deficiency (dMMR) is important for precision medicine. Tumor features, individually and in combination, derived from whole-exome sequenced (WES) colorectal cancers (CRCs) and panel-sequenced CRCs, endometrial cancers (ECs), and sebaceous skin tumors (SSTs) were assessed for their accuracy in detecting dMMR. CRCs (n = 300) with WES, where mismatch repair status was determined by immunohistochemistry, were assessed for microsatellite instability (MSMuTect, MANTIS, MSIseq, and MSISensor), Catalogue of Somatic Mutations in Cancer tumor mutational signatures, and somatic mutation counts. A 10-fold cross-validation approach (100 repeats) evaluated the dMMR prediction accuracy for i) individual features, ii) Lasso statistical model, and iii) an additive feature combination approach. Panel-sequenced tumors (29 CRCs, 22 ECs, and 20 SSTs) were assessed for the top performing dMMR predicting features/models using these three approaches. For WES CRCs, 10 features provided >80% dMMR prediction accuracy, with MSMuTect, MSIseq, and MANTIS achieving ≥99% accuracy. The Lasso model achieved 98.3% accuracy. The additive feature approach, with three or more of six of MSMuTect, MANTIS, MSIseq, MSISensor, insertion-deletion count, or tumor mutational signature small insertion/deletion 2 + small insertion/deletion 7 achieved 99.7% accuracy. For the panel-sequenced tumors, the additive feature combination approach of three or more of six achieved accuracies of 100%, 95.5%, and 100% for CRCs, ECs, and SSTs, respectively. The microsatellite instability calling tools performed well in WES CRCs; however, an approach combining tumor features may improve dMMR prediction in both WES and panel-sequenced data across tissue types.

Comprehensive Study of Microsatellite Instability Testing and Its Comparison With Immunohistochemistry in Gastric Cancers

PURPOSE

In this study, polymerase chain reaction (PCR)-based microsatellite instability (MSI) testing was comprehensively analyzed and compared with immunohistochemistry (IHC) for mismatch repair (MMR) protein expression in patients with gastric cancer (GC).

MATERIALS AND METHODS

In 5,676 GC cases, PCR-based MSI testing using five microsatellites (BAT-26, BAT-25, D5S346, D2S123, and D17S250) and IHC for MLH1 were performed. Re-evaluation of MSI testing/MLH1 IHC and additional IHC for MSH2, MSH6, and PMS2 were performed in discordant/indeterminate cases.

RESULTS

Of the 5,676 cases, microsatellite stable (MSS)/MSI-low and intact MLH1 were observed in 5,082 cases (89.5%), whereas MSI-high (MSI-H) and loss of MLH1 expression were observed in 502 cases (8.8%). We re-evaluated the remaining 92 cases (1.6%) with a discordant/indeterminate status. Re-evaluation showed 1) 37 concordant cases (0.7%) (18 and 19 cases of MSI-H/MMR-deficient (dMMR) and MSS/MMR-proficient (pMMR), respectively), 2) 6 discordant cases (0.1%) (3 cases each of MSI-H/pMMR and MSS/dMMR), 3) 14 MSI indeterminate cases (0.2%) (1 case of dMMR and 13 cases of pMMR), and 4) 35 IHC indeterminate cases (0.6%) (22 and 13 cases of MSI-H and MSS, respectively). Finally, MSI-H or dMMR was observed in 549 cases (9.7%), of which 47 (0.8%) were additionally confirmed as MSI-H or dMMR by re-evaluation. Sensitivity was 99.3% for MSI testing and 95.4% for MMR IHC.

CONCLUSIONS

Considering the low incidence of MSI-H or dMMR, discordant/indeterminate results were occasionally identified in GCs, in which case complementary testing is required. These findings could help improve the accuracy of MSI/MMR testing in daily practice.

Clinically relevant fusion oncogenes: detection and practical implications

Mechanistically, chimeric genes result from DNA rearrangements and include parts of preexisting normal genes combined at the genomic junction site. Some rearranged genes encode pathological proteins with altered molecular functions. Those which can aberrantly promote carcinogenesis are called fusion oncogenes. Their formation is not a rare event in human cancers, and many of them were documented in numerous study reports and in specific databases. They may have various molecular peculiarities like increased stability of an oncogenic part, self-activation of tyrosine kinase receptor moiety, and altered transcriptional regulation activities. Currently, tens of low molecular mass inhibitors are approved in cancers as the drugs targeting receptor tyrosine kinase (RTK) oncogenic fusion proteins, that is, including ALK, ABL, EGFR, FGFR1-3, NTRK1-3, MET, RET, ROS1 moieties. Therein, the presence of the respective RTK fusion in the cancer genome is the diagnostic biomarker for drug prescription. However, identification of such fusion oncogenes is challenging as the breakpoint may arise in multiple sites within the gene, and the exact fusion partner is generally unknown. There is no gold standard method for RTK fusion detection, and many alternative experimental techniques are employed nowadays to solve this issue. Among them, RNA-seq-based methods offer an advantage of unbiased high-throughput analysis of only transcribed RTK fusion genes, and of simultaneous finding both fusion partners in a single RNA-seq read. Here we focus on current knowledge of biology and clinical aspects of RTK fusion genes, related databases, and laboratory detection methods.

DNA Mismatch Repair Proteins and BRAF V600E Detection by Immunohistochemistry in Colorectal Cancer Demonstrates Concordance with Next Generation Sequencing

Background and Aims: Multiple laboratory methods are used to screen patients with colorectal cancer (CRC) for mismatch repair (MMR) protein deficiency to identify possible Lynch syndrome patients. The goal of this study was to compare the agreement between ready-to-use immunohistochemistry (IHC) assays for MLH-1, PMS-2, MSH-2, MSH-6, and mutated BRAF at V600E and molecular methods in CRC cases. The inclusion of the BRAF V600E mutation testing is important for the identification of patients with sporadic CRC, as the BRAF V600E mutation is very rarely observed in patients with Lynch syndrome tumors. Methods: CRC cases were analyzed by ColoSeqTM tumor sequencing assay and VENTANA MMR IHC Panel that included anti-MLH1, anti-PMS2, anti-MSH2, anti-MSH6, and anti-BRAF V600E antibodies. Additionally, CRC cases with MLH1 IHC loss were evaluated for MLH1 promoter hypermethylation. Results: One hundred and eighteen cases were analyzed. The overall percent agreement (OPA) for each evaluated marker status compared to next-generation sequencing (NGS) exceeded 96%. Twenty-three cases were positive for the BRAF V600E mutation by IHC and NGS, and twenty cases showed loss of MLH1 protein and were positive for MLH1 hypermethylation. Samples with loss of MMR protein expression by IHC demonstrated genetic and/or epigenetic alterations that were consistent with the observed protein expression patterns. Conclusions: The results of this study indicate that ready-to-use IHC assays can correctly identify the loss of MMR proteins and the presence of mutated BRAF V600E protein, supporting the utility of the VENTANA MMR IHC Panel as an aid to stratify patients with sporadic CRC vs. potential Lynch syndrome.

Molecular Targeted Therapy in Oncology Focusing on DNA Repair Mechanisms

DNA repair mechanisms are essential for maintaining cellular homeostasis. Malfunction of these repair mechanisms leads to cellular DNA mutations, carcinogenic transformation, and cell death. These same defects also create vulnerabilities that are relatively specific to cancer cells, and which could potentially be exploited to increase the therapeutic index of anticancer treatments and thereby improve patient outcomes. The targeted therapy based on inhibiting the DNA damage response (DDR) opens a new therapeutic landscape for patients with deficient DDR. Currently there are two DNA repair mechanisms that are used as targets for molecular therapies: Mitsmach Repair (MMR) and Homologous Recombination Repair (HRR). These molecular targets allow for immunotherapy treatments based on "checkpoint inhibitors" (ICIs) drugs and "PARP inhibitor" (PARPi) drugs in different solid tumors. In this review we will describe the state of the art of this interesting mechanism and explain the options for treatment based on these alterations. Moreover, many clinical trials are currently underway exploring better treatment options for dMMR and HRD patients with different solid tumours.

Role of PD-1/PD-L1-mediated tumour immune escape mechanism and microsatellite instability in the BCG failure of high-grade urothelial carcinomas

BACKGROUND

Intravesical BCG treatment fails inexplicably in 30%-45% of patients for high-grade nonmuscle-invasive bladder cancer (NMIBC). We aimed to investigate the role of PD-1/PD-L1 interaction on BCG failure of high-grade NMIBC and to identify biomarkers for predicting BCG responsive cases.

METHODS

Thirty BCG responsive and 29 nonresponsive NMIBCs were included in the study. Expressions of PDL1(SP-263), MSH2, MSH6, PMS2, and MLH1 were evaluated on pre- and post-BCG transurethral resection (TUR-B) specimens by immunohistochemistry. PD-L1(SP-263) expression was categorised as negative/low, high. DNA mismatch repair protein (MMR) expressions were classified as "reduced" if ≤30% of nuclei stained, "preserved" if >30% of nuclei stained. Microsatellite instability (MSI) testing was performed by PCR using five mononucleotide markers.

RESULTS

Reduced DNA MMR protein expression was found to be significantly higher in the pretreatment biopsies of BCG-responsive group than the BCG nonresponsive tumour group (p = 0.022). PD-L1 expression did not show any significant difference between the pre- and posttreatment TUR-B specimens of the BCG nonresponsive tumour group or between the pretreatment TUR-B specimens of BCG nonresponsive and the BCG responsive groups (p = 0.508, p = 0.708, respectively).

DISCUSSION

Immune escape of tumour cells by PD-1/PD-L1 interaction does not seem to have any role in BCG failure of NMIBCs. Reduced MMR expression may help to determine cases that will respond well to BCG therapy. A better antitumour activity of BCG in NMIBCs with reduced MMR expression may be related to the ongoing accumulation of cancer neoantigens in correlation with increased tumour mutation load as a result of DNA repair defects.

Serplulimab, a novel anti-PD-1 antibody, in patients with microsatellite instability-high solid tumours: an open-label, single-arm, multicentre, phase II trial

BACKGROUND

Microsatellite instability-high/mismatch repair-deficient (MSI-H/dMMR) tumours have a high response rate to immunotherapy. Antitumour activity and safety of serplulimab, a novel humanised anti-PD-1 monoclonal antibody, were evaluated in this phase II study.

METHODS

In this ongoing, single-arm, open-label, phase II trial, patients with previously treated unresectable or metastatic MSI-H/dMMR solid tumours received intravenous serplulimab 3 mg/kg every 2 weeks for up to 52 cycles. The primary endpoint was objective response rate (ORR) assessed by an independent radiological review committee per Response Evaluation Criteria in Solid Tumors v1.1. Secondary endpoints included additional efficacy measures, safety, and tolerability.

RESULTS

As of 9 January 2021, 108 patients were enrolled, and 68 patients with confirmed MSI-H solid tumours were included in the main efficacy analysis population (MEAP). The median follow-up duration in the MEAP was 7.7 months, with an ORR of 38.2% (95% confidence interval, 26.7-50.8). Of the 108 patients, grade ≥3 treatment-emergent adverse events were reported in 53 (49.1%) patients; immune-related adverse events occurred in 52 (48.1%) patients.

CONCLUSIONS

Serplulimab demonstrates a durable antitumour effect and a manageable safety profile in previously treated patients with MSI-H solid tumours. Serplulimab is a promising tissue-agnostic treatment for previously treated MSI-H solid tumours.

TRIAL REGISTRATION

NCT03941574.

Detecting mismatch repair deficiency in solid neoplasms: immunohistochemistry, microsatellite instability, or both?

In managing patients with solid tumors, the value of detecting the status of tumor DNA mismatch repair function is widely recognized. Mismatch repair protein immunohistochemistry and molecular microsatellite instability testing constitute the two major test modalities currently in use, yet each is associated with caveats and limitations that can be consequential. Most notably, the traditional approach of defining mismatch repair protein immunohistochemistry abnormality by complete loss of staining in all tumor cells is evolving. Partial or clonal loss is becoming recognized as a manifestation of gene abnormality; in some cases, such clonal loss is associated with germline pathogenic variants. The current criteria and cutoff values for defining microsatellite instability-high are developed primarily according to colorectal tumors. Non-colorectal cases, and occasionally even colorectal tumors, that are mismatch repair-deficient by immunohistochemistry but not microsatellite instability-high by current standards are being recognized. Emerging data suggest that these immunohistochemistry abnormal / non-microsatellite instability-high cases warrant further genetic workup for Lynch syndrome detection. Whether these tumors respond to immunotherapy is a question still to be addressed. It is imperative that pathologists as well as clinicians and investigators be aware of such intricacies regarding routine immunohistochemistry and microsatellite instability testing and the results they generate. This review summarizes our current understanding of the advantages and limitations of these tests and offer our view on what constitutes the most optimal strategy in test selection and how best to utilize case context to enhance the interpretation of the test results.

Combining inhibition of immune checkpoints and PARP: rationale and perspectives in cancer treatment

INTRODUCTION

Genomic instability resulting from the inability of cells to repair DNA damage is a breeding ground for immune checkpoint inhibitors (ICIs) and targeted treatments. Poly (ADP-ribose) polymerase inhibitors (PARPi) interfere with the efficient repair of DNA single-strand break damage inducing, mainly in tumors with existing defects in double strand DNA repair system, synthetic lethality.

AREAS COVERED

By amplifying the DNA damage and inducing immunogenic cell death PARPi leads tumor neoantigens to increase, upregulation of programmed death-ligand 1, and modulation of the tumor microenvironment facilitating a more intense antitumor immune response. In this review, we reported the immunological role of PARPi and the rational use of the combination with ICIs, evaluating data from combination clinical trials and discussing perspectives.

EXPERT OPINION

Several prospective combination studies to overcome existing limitations to PARPi and ICI single agents are currently ongoing. The identification of the different resistance mechanisms to PARPi and ICI as well as the development of accurate and predictive biomarkers of response should be a priority to identify the patients who may most benefit from this combination. Similarly, clarifying the role and interaction between the DNA damage repair pathways and the tumor immune microenvironment would increase success of the combination.

MSI colorectal cancer, all you need to know

Colorectal cancer management has been dramatically impacted by molecular profiling these last years. Among these molecular subgroups, patients with microsatellite instability (MSI) are of particular interest, owing to the prognostic and predictive value of this tumor biomarker. This review article explains the molecular abnormalities underlying MSI phenotype and the consequences of such molecular abnormalities on carcinogenesis, genetic instability and immune infiltration. It details the diagnostic methods for identifying MSI colorectal cancer patients and describes how the prognostic and theranostic values of this marker are impacting treatment decision-making for these patients in 2022.