Serendipity Strikes: How Pursuing Novel Hypotheses Shifted the Paradigm Regarding the Genetic Basis of Colorectal Cancer and Changed Cancer Therapy

In this installment of the "Paradigm Shifts in Perspective" series, the authors, all scientists who have been involved in colorectal cancer (CRC) research for most or all of their careers, have watched the field develop from early pathological descriptions of tumor formation to the current understanding of tumor pathogenesis that informs personalized therapies. We outline how our understanding of the pathogenetic basis of CRC began with seemingly isolated discoveries-initially with the mutations in RAS and the APC gene, the latter of which was initially found in the context of intestinal polyposis, to the more complex process of multistep carcinogenesis, to the chase for tumor suppressor genes, which led to the unexpected discovery of microsatellite instability (MSI). These discoveries enabled the authors to better understand how the DNA mismatch repair (MMR) system not only recognizes DNA damage but also responds to damage by DNA repair or by triggering apoptosis in the injured cell. This work served, in part, to link the earlier findings on the pathogenesis of CRC to the development of immune checkpoint inhibitors, which has been transformative-and curative-for certain types of CRCs and other cancers as well. These discoveries also highlight the circuitous routes that scientific progress takes, which can include thoughtful hypothesis testing and at other times recognizing the importance of seemingly serendipitous observations that substantially change the flow and direction of the discovery process. What has happened over the past 37 years was not predictable when this journey began, but it does speak to the power of careful scientific experimentation, following the facts, perseverance in the face of opposition, and the willingness to think outside of established paradigms.

Efficiency of CT radiomics model in assessing the microsatellite instability of colorectal cancer liver metastasis

OBJECTIVE

This study aims to investigate the efficiency of a radiomics model in identifying high-frequency microsatellite instability (MSI-H) and microsatellite stability (MSS) of colorectal liver metastasis (CRLM) according to machine learning radiomics features of enhanced CT liver images.

MATERIALS AND METHODS

A total of 12 patients with MSI-H CRLM and 96 patients with MSS CRLM were randomly divided into the training group and internal validation group according to the ratio of 7: 3 (training: 75 cases, validation: 33 cases). From the enhanced CT (portal phase) image data of patients, 788 radiomics features were extracted, and a random forest model was established with the optimal features selected. The receiver operating characteristics (ROC) curve analysis was performed to assess the model's diagnostic efficacy.

RESULTS

The training group comprised 8 patients with MSI-H CRLM and 67 patients with MSS CRLM, and the internal validation group included 4 patients with MSI-H CRLM and 29 patients with MSS CRLM. After feature selection, 7 radiomics features good for distinguishing MSI-H CRLM and MSS CRLM were screened out. The ROC curve analysis demonstrated that the random forest model had the AUC (area under the ROC curve) value 0.88, accuracy 0.85, sensitivity 0.85, specificity 0.92, and F1 score 0.88 in the training group. The model had an AUC value of 0.75, accuracy of 0.74, sensitivity of 0.81, specificity of 0.85, and F1_score of 0.78 in the internal validation group in identifying the MSI-H from the MSS CRLM. In order to evaluate the robustness of the overall model, the 788 features obtained were all applied to the 5-fold cross-validation, with the model being built on the random forest and analyzed with the ROC curve analysis. The AUC value of the model was 0.86 (P＜0.05), accuracy value 0.91, sensitivity 0.60, and specificity 0.95.

CONCLUSION

The random forest prediction model built on the radiometric features extracted from enhanced CT images can be used to identify the MSI-H from the MSS CRLM and may provide effective guidance for clinical immunotherapy of CRLM patients with unknown MSI status.

Neoadjuvant anti-PD-1/PD-L1 therapy for colorectal cancer: Current status and future prospects

Immunotherapy, particularly programmed cell death 1/programmed cell death ligand 1 (PD-1/PD-L1) inhibitors, has made revolutionary progress in the treatment strategies for various types of cancer. Regarding colorectal cancer (CRC), the current clinical application of PD-1/PD-L1 inhibitors is primarily categorized based on mutation patterns, including deficient mismatch repair (dMMR)/high microsatellite instability (MSI-H) and proficient mismatch repair (pMMR) or non-high microsatellite instability (non-MSI-H). PD-1/PD-L1 inhibitors have demonstrated good efficacy against dMMR/MSI-H CRC by increasing T-cell infiltration into tumor tissues. However, the effectiveness of PD-1/PD-L1 inhibitors for pMMR/non-MSI-H CRC remains uncertain. Due to the lower prevalence of dMMR/MSI-H in CRC, recent clinical trials have reported combined applications of PD-1/PD-L1 inhibitors with other anti-tumor treatments such as chemotherapy, radiotherapy, and targeted therapy to achieve better therapeutic outcomes. Neoadjuvant therapy, primarily consisting of chemotherapy and radiotherapy, not only downstages the tumor but also provides benefits from local control, thus improving clinical symptoms and quality of life. Integrating immunotherapy into neoadjuvant therapy may alter the treatment approach for potentially resectable or certain metastatic CRC cases. In this article, we focus on the development of neoadjuvant anti-PD-1/PD-L1 therapy and discuss its future prospects for the treatment of CRC.

Microsatellite instability and sex-specific differences of survival in gastric cancer after neoadjuvant chemotherapy without and with taxane: An observational study in real world patients

PURPOSE

To investigate the prognostic role of microsatellite instability (MSI) in association with sex of patients treated with platinum/fluoropyrimidine neoadjuvant chemotherapy (CTx) with or without a taxane-containing compound.

METHODS

Of the 505 retrospectively analyzed patients with gastric or gastroesophageal adenocarcinoma, 411 patients were treated without taxane and 94 patients with a taxane-containing compound. MSI was determined using standard assays.

RESULTS

Females demonstrated a better overall survival (OS) than males in the non-taxane group (HR, 0.59; 95% CI 0.41-0.86; p = 0.005), whereas no significant difference was found in the taxane group (HR 1.22; 95% CI 0.55-2.73, p = 0.630). MSI-High (-H) was associated with a better prognosis in both groups (without taxane: HR 0.56; 95% CI 0.33-0.97; p = 0.038; with taxane: HR 0.28; 95% CI 0.04-2.02, p = 0.204). In the non-taxane group, female MSI-H patients showed the best OS (HR 0.18, 95% CI 0.05-0.73; p = 0.016), followed by the female microsatellite stable (MSS) (HR 0.67, 95% CI 0.46-0.98, p = 0.040) and the male MSI-H group (HR 0.76; 95% CI 0.42-1.37, p = 0.760) taken the male MSS group as reference. In the taxane group, female and male MSI-H patients demonstrated the best OS (female MSI-H: HR 0.05, 95% CI 0.00-240.46; male MSI-H: HR 0.45, 95% CI 0.61-3.63, p = 0.438), whereas the female MSS group showed a decreased OS (HR 1.39 95% CI 0.62-3.12, p = 0.420) compared to male MSS patients.

CONCLUSION

OS in gastric/gastroesophageal cancer after CTx might depend on sex and MSI status and may differ between patients treated with or without a taxane compound in the chemotherapeutic regimen.

Heterogeneous expression of mismatch repair proteins and interpretation of immunohistochemical results in colorectal cancer and endometrial cancer

To investigate the heterogeneous expression patterns of four mismatch repair (MMR) proteins in colorectal cancer (CRC) and endometrial cancer (EC), and their effects on the interpretation of immunohistochemical (IHC) results. A total of 1636 CRC and EC specimens were collected from two hospitals. Seventy-eight cases had heterogeneous expression of MMR proteins, including 49 CRC and 29 EC cases. Polymerase chain reaction-capillary electrophoresis (PCR-CE) was then performed to detect the microsatellite instability (MSI) status, and 44 cases were further verified by targeted next-generation sequencing (NGS). Heterogeneous expression of MMR proteins was observed in 66 cases (66/78, 84.6%) of proficient MMR (pMMR) and 12 cases (12/78, 15.4%) of deficient MMR (dMMR). The proportion of heterogeneous MMR protein expression in EC (12.0%) was higher than that in CRC (3.5%). The heterogeneous expression patterns were divided into focal clonal heterogeneity (6/78, 7.7%) and glandular mosaic heterogeneity (72/78, 92.3%). Surprisingly, three pMMR CRC cases showed isolated small focal clonal heterogeneity of mutS homologue 6 (MSH6), with < 15% positive tumour cells, which was validated as high MSI (MSI-H) with PCR-CE and NGS. However, the other three EC pMMR cases with > 50% focal clonal heterogeneity of MMR proteins were verified as microsatellite stable (MSS) or low MSI (MSI-L). Fifteen EC cases with glandular mosaic heterogeneous expression of MMR proteins included two MSI-H cases, which were validated using PCR-CE and NGS. Among the dMMR cases, only two EC cases with mutL homologue 1 (MLH1)/PMS1 homologue 2, mismatch repair system component (PMS2) loss and MSH2/MSH6 mosaic heterogeneous expression were confirmed as MSS using PCR-CE and NGS, which may be related to the mechanism of MLH1 promoter methylation. Thus, in CRC, only cases with small focal clonal heterogeneous expression of MSH6 have a high likelihood of MSI-H, and further PCR-CE or NGS testing is recommended. The possibility of MSI-H cannot be ruled out in EC cases with glandular mosaic heterogeneous expression of MMR proteins; PCR-CE or NGS detection is therefore necessary.

Assessment of the reliability of MSI status and dMMR proteins deficiency screening on endoscopic biopsy material in esophagus and gastric adenocarcinoma

BACKGROUND

Microsatellite instability (MSI) is a negative predictive factor for neoadjuvant chemotherapy in resectable oesogastric adenocarcinoma and a crucial determinant for immunotherapy. We aimed to evaluate reliability of dMMR/MSI status screening performed on preoperative endoscopic biopsies.

METHODS

Paired pathological samples from biopsies and surgical specimen of oesogastric adenocarcinoma were retrospectively collected between 2009 and 2019. We compared dMMR status obtained by immunohistochemistry (IHC) and MSI status by PCR. dMMR/MSI status on surgical specimen was considered as reference.

RESULTS

PCR and IHC were conclusive on biopsies respectively for 53 (96.4%) and 47 (85.5%) of the 55 patients enrolled. IHC was not contributive for 1 surgical specimen. A third reading of IHC was carried out for 3 biopsies. MSI status was observed in 7 (12.5%) surgical specimens. When analyses were contributive, sensitivity and specificity of biopsies for dMMR/MSI were respectively 85% and 98% for PCR vs. 86% and 98% for IHC. Concordance rate between biopsies and surgical specimen was 96.2% for PCR and 97.8% for IHC.

CONCLUSIONS

Endoscopic biopsies are a suitable source of tissue for dMMR/MSI status determination in oesogastric adenocarcinoma which should be routinely performed at diagnosis to better adapt neoadjuvant treatment.

MINIABSTRACT

By comparison of dMMR phenotype obtained by immunohistochemistry and MSI status by PCR between match-paired samples of oesogastric cancer's endoscopic biopsies and surgical specimen, we observed that biopsies are a suitable source of tissue for dMMR/MSI status determination.

A review of basic to clinical targeted therapy and immunotherapy in uterine serous cancer

Uterine serous carcinomas show more frequent mutations of TP53, FBXW7, PIK3CA, and PP2R1A. Furthermore, cyclin-dependent kinase, human epidermal growth factor receptor 2, phosphatidylinositol 3-kinase/protein kinase B, and mammalian target of rapamycin signaling pathways are involved in uterine serous carcinoma progression. However, most patients with uterine serous carcinoma develop chemoresistance to paclitaxel and carboplatin. Moreover, uterine serous carcinoma shows immunosuppressive microenvironment with lower frequency of microsatellite instability. However, some clinical trials of human epidermal growth factor receptor 2/neu and WEE1 targeted therapies showed good effects in prolonging the survival in patients with uterine serous carcinoma. More effective targeted therapies and immunotherapies need to be developed in recurrent uterine serous carcinomas.

SETD2 variation correlates with tumor mutational burden and MSI along with improved response to immunotherapy

BACKGROUND

SETD2 protects against genomic instability via maintenance of homologous recombination repair (HRR) and mismatch repair (MMR) in neoplastic cells. However, it remains unclear whether SETD2 dysfunction is a complementary or independent factor to microsatellite instability-high (MSI-H) and tumor mutational burden-high (TMB-H) for immunocheckpoint inhibitor (ICI) treatment, and little is known regarding whether this type of dysfunction acts differently in various types of cancer.

METHODS

This cohort study used multidimensional genomic data of 6726 sequencing samples from our cooperative and non-public GenePlus institute from April 1 through April 10, 2020. MSIsensor score, HRD score, RNAseq, mutational data, and corresponding clinical data were obtained from the TCGA and MSKCC cohort for seven solid tumor types.

RESULTS

A total of 1021 genes underwent target panel sequencing reveal that SETD2 mutations were associated with a higher TMB. SETD2 deleterious mutation dysfunction affected ICI treatment prognosis independently of TMB-H (p < 0.01) and had a lower death hazard than TMB-H in pancancer patients (0.511 vs 0.757). Significantly higher MSI and lower homologous recombination deficiency were observed in the SETD2 deleterious mutation group. Improved survival rate was found in the MSKCC-IO cohort (P < 0.0001) and was further confirmed in our Chinese cohort.

CONCLUSION

We found that SETD2 dysfunction affects ICI treatment prognosis independently of TMB-H and has a lower death hazard than TMB-H in pancancer patients. Therefore, SETD2 has the potential to serve as a candidate biomarker for ICI treatment. Additionally, SETD2 should be considered when dMMR is detected by immunohistochemistry.

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.

The role of heavy metals in the development of colorectal cancer

OBJECTIVE

To investigate the relationship among 18 heavy metals, microsatellite instability (MSI) status, ERCC1, XRCC1 (rs25487), BRAF V600E and 5 tumor markers and their role in the development of colorectal cancer (CRC).

METHODS

A total of 101 CRC patients and 60 healthy controls were recruited in the present study. The levels of 18 heavy metals were measured by ICP-MS. MSI status and the genetic polymorphism were determined by PCR (FP205-02, Tiangen Biochemical Technology Co., Ltd., Beijing, China) and Sanger sequencing. Spearman's rank correlation was used to analyze the relationship among various factors.

RESULTS

The level of selenium (Se) was lower in the CRC group compared with the control group (p < 0.01), while vanadium (V), arsenic (As), tin (Sn), barium (Ba) and lead (Pb) were higher (p < 0.05), chromium (Cr) and copper (Cu) were significantly higher (p < 0.0001) in the CRC group than those in the control group. Multivariate logistic regression analysis indicated that Cr, Cu, As and Ba were the risk factors for CRC. In addition, CRC was positively correlated with V, Cr, Cu, As, Sn, Ba and Pb, but negatively correlated with Se. MSI was positively correlated with BRAF V600E, but negatively correlated with ERCC1. BRAF V600E was positively correlated with antimony (Sb), thallium (Tl), CA19-9, NSE, AFP and CK19. XRCC1 (rs25487) was found to be positively correlated with Se but negatively correlated with Co. The levels of Sb and Tl were significantly higher in the BRAF V600E positive group compared to the negative group. The mRNA expression level of ERCC1 was significantly higher (P = 0.035) in MSS compared to MSI. And there was a significant correlation between XRCC1 (rs25487) polymorphism and MSI status (P<0.05).

CONCLUSION

The results showed that low level of Se and high levels of V, As, Sn, Ba, Pb, Cr, and Cu increased the risk of CRC. Sb and Tl may cause BRAF V600E mutations, leading to MSI. XRCC1 (rs25487) was positively correlated with Se but negatively correlated with Co. The expression of ERCC1 may be related to MSS, while the XRCC1 (rs25487) polymorphism is related to MSI.

Tumour mutational burden as a biomarker in patients with mismatch repair deficient/microsatellite instability-high metastatic colorectal cancer treated with immune checkpoint inhibitors

BACKGROUND

Immune checkpoint inhibitors (ICIs) are the standard treatment in patients with mismatch repair deficient (dMMR)/microsatellite instability-high (MSI-H) metastatic colorectal cancer (mCRC). Tumour mutational burden (TMB) is a promising biomarker for the prediction of treatment outcomes.

PATIENTS AND METHODS

We screened 203 patients with dMMR/MSI-H mCRC treated with an anti-PD-(L)1 (anti-Programmed-Death-(Ligand)1) plus or minus an anti-Cytotoxic T-Lymphocyte Antigen 4 (anti-CTLA-4) agent at three Italian Academic Centers. TMB was tested by Foundation One Next Generation Sequencing assay and correlated with clinical outcomes, in the overall population and according to ICI regimen.

RESULTS

We included 110 patients with dMMR/MSI-H mCRC. Eighty patients received anti-PD-(L)1 monotherapy and 30 received anti-CTLA-4 combinations. Median TMB was 49 mut/Mb (range: 8-251 mut/Mb). The optimal prognostic cut-off for progression-free survival (PFS) stratification was 23 mut/Mb. Patients with TMB ≤23 mut/Mb had significantly worse PFS (adjusted Hazard Ratio [aHR] = 4.26, 95% confidence interval [CI]:1.85-9.82, p = 0.001) and overall survival (OS) (aHR = 5.14, 95% CI: 1.76-14.98, p = 0.003). Using a cut-off optimised for predicting treatment outcome, anti-CTLA-4 combination was associated with a significant PFS/OS benefit versus anti-PD-(L)1 monotherapy in patients with TMB>40 mut/Mb (2-year PFS: 100.0% versus 70.7%, p = 0.002; 2-year OS: 100.0% versus 76.0%, p = 0.025), but not in those with TMB ≤40 mut/Mb (2-year PFS: 59.7% versus 68.6%, p = 0.888; 2-year OS: 80.0% versus 81.0%, p = 0.949).

CONCLUSION

Patients with dMMR/MSI-H mCRC and relatively lower TMB value displayed early disease progression when receiving ICIs, whereas patients with the highest TMB values may obtain the maximal benefit from intensified anti-CTLA-4/PD-1 combination.

Increased Fusobacterium tumoural abundance affects immunogenicity in mucinous colorectal cancer and may be associated with improved clinical outcome

There is currently an urgent need to identify factors predictive of immunogenicity in colorectal cancer (CRC). Mucinous CRC is a distinct histological subtype of CRC, associated with a poor response to chemotherapy. Recent evidence suggests the commensal facultative anaerobe Fusobacterium may be especially prevalent in mucinous CRC. The objectives of this study were to assess the association of Fusobacterium abundance with immune cell composition and prognosis in mucinous CRC. Our study included two independent colorectal cancer patient cohorts, The Cancer Genome Atlas (TCGA) cohort, and a cohort of rectal cancers from the Beaumont RCSI Cancer Centre (BRCC). Multiplexed immunofluorescence staining of a tumour microarray (TMA) from the BRCC cohort was undertaken using Cell DIVE technology. Our cohorts included 87 cases (13.3%) of mucinous and 565 cases (86.7%) of non-mucinous CRC. Mucinous CRC in the TCGA dataset was associated with an increased proportion of CD8 + lymphocytes (p = 0.018), regulatory T-cells (p = 0.001) and M2 macrophages (p = 0.001). In the BRCC cohort, mucinous RC was associated with enhanced CD8 + lymphocyte (p = 0.022), regulatory T-cell (p = 0.047), and B-cell (p = 0.025) counts. High Fusobacterium abundance was associated with an increased proportion of CD4 + lymphocytes (p = 0.031) and M1 macrophages (p = 0.006), whilst M2 macrophages (p = 0.043) were under-represented in this cohort. Patients with increased Fusobacterium relative abundance in our mucinous CRC TCGA cohort tended to have better clinical outcomes (DSS: likelihood ratio p = 0.04, logrank p = 0.052). Fusobacterium abundance may be associated with improved outcomes in mucinous CRC, possibly due to a modulatory effect on the host immune response. KEY MESSAGES: • Increased Fusobacterium relative abundance was not found to be associated with microsatellite instability in mucinous CRC. • Increased Fusobacterium relative abundance was associated with an M2/M1 macrophage switch, which is especially significant in mucinous CRC, where M2 macrophages are overexpressed. • Increased Fusobacterium relative abundance was associated with a significant improvement in disease specific survival in mucinous CRC. • Our findings were validated at a protein level within our own in house mucinous and non-mucinous rectal cancer cohorts.

Evaluating mismatch repair deficiency in colorectal cancer biopsy specimens

Mismatch repair (MMR) testing on all new cases of colorectal cancer (CRC) has customarily been preferably performed on surgical specimens, as more tissue is available; however, new clinical trials for the use of immune checkpoint inhibitors in the neoadjuvant setting require MMR testing on biopsy samples. This study aims at identifying advantages, disadvantages and any potential pitfalls in MMR evaluation on biopsy tissue and how to cope with them. The study is prospective-retrospective, recruiting 141 biopsies (86 proficient (p)MMR and 55 deficient (d)MMR) and 97 paired surgical specimens (48 pMMR; 49 dMMR). In biopsy specimens, a high number of indeterminate stains was observed, in particular for MLH1 (31 cases, 56.4%). The main reasons were a punctate nuclear expression of MLH1, relatively weak MLH1 nuclear expression compared to internal controls, or both (making MLH1 loss difficult to interpret), which was solved by reducing primary incubation times for MLH1. A mean of  ≥ 5 biopsies had adequate immunostains, compared to ≤ 3 biopsies in inadequate cases. Conversely, surgical specimens rarely suffered from indeterminate reactions, while weaker staining intensity (p < 0.007) for MLH1 and PMS2 and increased patchiness grade (p < 0.0001) were seen. Central artefacts were almost exclusive to surgical specimens. MMR status classification was possible in 92/97 matched biopsy/resection specimen cases, and all of these were concordant (47 pMMR and 45 dMMR). Evaluation of MMR status on CRC biopsy samples is feasible, if pitfalls in interpretation are known, making laboratory-specific appropriate staining protocols fundamental for high-quality diagnoses.

Performance of Immunohistochemical and Molecular Methods in Detecting Microsatellite Instability in Gastric Cancer: A Multicenter Study

INTRODUCTION

Microsatellite instability (MSI) is an important prognostic molecular biomarker for gastric cancer (GC). MSI status may be detected by immunohistochemistry (IHC) for mismatch repair (MMR) proteins and polymerase chain reaction (PCR). Idylla™ MSI assay has not been validated for GC but may prove to be a valid alternative.

METHODS

In a series of 140 GC cases, MSI status was evaluated by IHC for MLH1, PMS2, MSH2, and MSH6; gold-standard pentaplex PCR panel (PPP) (BAT-25, BAT-26, NR-21, NR-24, and NR-27); and Idylla. Statistical analysis was performed using SPSS 27.0.

RESULTS

PPP identified 102 microsatellite stable (MSS) cases and 38 MSI-high cases. Only 3 cases showed discordant results. Compared with PPP, the sensitivity was 100% for IHC and 94.7% for Idylla. Specificity was 99% for IHC and 100% for Idylla. MLH1 IHC alone showed sensitivity and specificity of 97.4% and 98.0%, respectively. IHC identified three indeterminate cases; all were MSS according to PPP and Idylla.

CONCLUSION

IHC for MMR proteins represents an optimal screening tool for MSI status in GC. If resources are limited, isolated MLH1 evaluation may constitute a valuable option for preliminary screening. Idylla may help detect rare MSS cases with MMR-loss and define MSI status in indeterminate cases.

Pre- and Postoperative Levels of Carcinoembryonic Antigen in Microsatellite Stable Versus Instable Colon Cancer: a Retrospective Analysis

PURPOSE

The prognosis of microsatellite stable (MSS) versus instable (MSI) tumors is an ongoing matter of debate, with differences in expression of carcinoembryonic antigen (CEA) in these two tumor subsets being inconsistently reported to date. The aim of this study was to investigate CEA expression in the context of clinical parameters in MSS and MSI tumors.

METHODS

Clinical, pathological, and biochemical parameters of colon cancer patients who underwent curative surgery were documented in a database and compared between MSS and MSI cases. The pre- to postoperative trend of CEA was analyzed. Survival was assessed using the Kaplan-Meier (log rank) test.

RESULTS

One hundred sixty-nine patients were included in the study. Compared to those with MSS tumors, there was a higher proportion of preoperatively elevated CEA among those with MSI tumors (p = 0.067). Median CEA values decreased over the pre- to postoperative course with MSS (p = 0.01) but not MSI (p = 0.093) tumors. The distribution of N classification differed between MSS and MSI tumors (p = 0.014). Patients with MSI tumors had superior survival.

CONCLUSION

Despite the better prognosis, MSI tumors are associated with increases in CEA. Our findings shed light on discrepancies related to the prognostic evaluation of MSI tumors. Furthermore, in follow-up of colorectal cancers, CEA measurements should be interpreted differently for MSI and MSS tumors.

Deep learning-based methods for classification of microsatellite instability in endometrial cancer from HE-stained pathological images

BACKGROUND

Microsatellite instability (MSI) is one of the essential tumor biomarkers for cancer treatment and prognosis. The presence of more significant PD-L1 expression on the surface of tumor cells in endometrial cancer with MSI suggests that MSI may be a promising biomarker for anti-PD-1/PD-L1 immunotherapy. However, the conventional testing methods are labor-intensive and expensive for patients.

METHODS

Inspired by classifiers for MSI based on fast and low-cost deep-learning methods in previous investigations, a new architecture for MSI classification based on an attention module is proposed to extract features from pathological images. Especially, slide-level microsatellite status will be obtained by the bag of words method to aggregate probabilities predicted by the proposed model. The H&E-stained whole slide images (WSIs) from The Cancer Genome Atlas endometrial cohort are collected as the dataset. The performances of the proposed model were primarily evaluated by the area under the receiver-operating characteristic curve, accuracy, sensitivity, and F1-Score.

RESULTS

On the randomly divided test dataset, the proposed model achieved an accuracy of 0.80, a sensitivity of 0.857, a F1-Score of 0.826, and an AUROC of 0.799. We then visualize the results of the microsatellite status classification to capture more specific morphological features, helping pathologists better understand how deep learning performs the classification.

CONCLUSIONS

This study implements the prediction of microsatellite status in endometrial cancer cases using deep-learning methods directly from H&E-stained WSIs. The proposed architecture can help the model capture more valuable features for classification. In contrast to current laboratory testing methods, the proposed model creates a more convenient screening tool for rapid automated testing for patients. This method can potentially be a clinical method for detecting the microsatellite status of endometrial cancer.

Discrepancy among microsatellite instability detection methodologies in non-colorectal cancer: Report of 3 cases

BACKGROUND

Microsatellite instability (MSI) is a predictive biomarker for cancer immunotherapy. The tumor-agnostic nature of MSI makes it a denominator for immunotherapy in several solid tumors. It can be assessed using next-generation sequencing (NGS), fluorescent multiplex PCR, and immunohistochemistry (IHC).

CASE SUMMARY

Here, we report 3 cases with discordant MSI results detected using different methods. A cholangiocellular carcinoma case revealed proficient mismatch repair (MMR) by IHC but high MSI (MSI-H) by liquid NGS. A cervical cancer case revealed deficient MMR by IHC, microsatellite stable by PCR, and MSI-H by NGS. Lastly, an endometrial cancer case revealed proficient MMR by IHC but MSI-H by NGS.

CONCLUSION

IHC for MMR status is the first choice due to several advantages. However, in cases of indeterminate IHC results, molecular testing by MSI-PCR is preferred. Recently, NGS-based MSI assays are being widely used to detect MSI-H tumors. All three methods have high accuracy; however, the inconsistencies between them may lead to misdiagnosis.

Microsatellite Instability with BRAF V600E Associated with Delayed Presentation but Poor Survival in Stage III Colorectal Cancer

Colorectal cancer (CRC) has tremendous molecular and genetic heterogeneity, making it a difficult cancer to treat. Two of the key prognostic indicators of CRC include microsatellite instability (MSI) and BRAF V600E mutation. Here, we performed a retrospective survival analysis on 145 stage II and III CRC patients treated at the University of Kansas Cancer Center between 2009 and 2020. Of the 145 patients, BRAF V600E was observed in 15% patients and MSI in 28% patients. Median survival was not reached for stage II. For stage III, patients with BRAF V600E showed poor overall survival, which worsened with concurrent presence of MSI [χ2=6.4, p=0.01]. Eighty-five percent of this group was found to have right-sided CRC. For stage III, overall survival (OS) was 27 months, 37 months, 87 months and not reached for MSI-H/BRAF V600E, MSS/BRAF V600E, MSS/BRAF WT and MSI-H/BRAF WT, respectively. Although associated with poor prognosis, presence of MSI in BRAF V600E patients was associated with delayed disease presentation (mean age 77) compared to those with stable microsatellite (mean age 63) [p=0.01]. Although median survival between the groups could not be assessed for stage II due to very few deaths and/or inadequate length of study, comparison of survival trend suggests that BRAF V600E, rather than MSI, is what drives prognosis in stage II CRC. Our findings suggest that prognostic value of MSI is more relevant for stage III than stage II CRC. Patients with MSI-H and BRAF V600E have advantage of late presentation, although at the cost of poor overall prognosis.

[Analysis of microsatellite instability in endometrial cancer: The significance of minimal microsatellite shift]

OBJECTIVE

To analyze the differences and characteristics of microsatellite instability (MSI) in endometrial cancer (EMC), by using colorectal cancer (CRC) as control.

METHODS

In the study, 228 cases of EMC were collected. For comparative analysis, 770 cases of CRC were collected. Mismatch repair (MMR) expression was detected by immunohistochemistry (IHC), and microsatellite instability (MSI) was analyzed by PCR and capillary electrophoresis fragment analysis (MSI-PCR). MSI-PCR was detected using five mononucleotide repeat markers: BAT-25, BAT-26, NR-21, NR-24, and MONO-27.

RESULTS

In EMC, we found 27.19% (62/228) of deficient mismatch repair (dMMR) using IHC, significantly higher than CRC (7.79%, 60/770). Meanwhile, subclonal expression of MMR protein was found in 4 cases of dMMR-EMC and 2 cases of dMMR-CRC. According to the criteria of major micro-satellite shift, we found 16.23% (37/228) of MSI-high (MSI-H), 2.63% (6/228) of MSI-low (MSI-L), and 81.14% (185/228) of microsatellite stability (MSS) in EMC using MSI-PCR. The discor-dance rate between MMR-IHC and MSI-PCR in EMC was 11.84% (27/228). In CRC, we found 8.05% (62/770) of MSI-H, 0.13% (1/770) of MSI-L, and 91.82% (707/770) of MSS. The discordance rate between MMR-IHC and MSI-PCR in CRC was only 0.52% (4/770). However, according to the criteria of minimal microsatellite shift, 12 cases of EMC showed minimal microsatellite shift including 8 cases of dMMR/MSS and 4 cases of dMMR/MSI-L and these cases were ultimately evaluated as dMMR/MSI-H. Then, 21.49% (49/228) of EMC showed MSI-H and the discordance rate MMR-IHC and MSI-PCR in EMC decreased to 6.58% (15/228). No minimal microsatellite shift was found in CRC. Compared with EMC group with major microsatellite shift, cases with minimal microsatellite shift showed younger age, better tumor differentiation, and earlier International Federation of Gynecology and Obstetrics (FIGO) stage. There were significant differences in histological variant and FIGO stage between the two groups (P < 0.001, P=0.006).

CONCLUSION

EMC was more prone to minimal microsatellite shift, which should not be ignored in the interpretation of MSI-PCR results. The combined detection of MMR-IHC and MSI-PCR is the most sensitive and specific method to capture MSI tumors.

Identification of mitochondrial respiratory chain signature for predicting prognosis and immunotherapy response in stomach adenocarcinoma

Stomach adenocarcinoma (STAD) is the third leading cause of cancer-related deaths and the fifth most prevalent malignancy worldwide. Mitochondrial respiratory chain complexes play a crucial role in STAD pathogenesis. However, how mitochondrial respiratory chain complex genes (MRCCGs) affect the prognosis and tumor microenvironment in STAD remains unclear. In this study, we systematically analyzed genetic alterations and copy number variations of different expression densities of MRCCGs, based on 806 samples from two independent STAD cohorts. Then we employed the unsupervised clustering method to classify the samples into three expression patterns based on the prognostic MRCCG expressions, and found that they were involved in different biological pathways and correlated with the clinicopathological characteristics, immune cell infiltration, and prognosis of STAD. Subsequently, we conducted a univariate Cox regression analysis to identify the prognostic value of 1175 subtype-related differentially expressed genes (DEGs) and screened out 555 prognostic-related genes. Principal component analysis was performed and developed the MG score system to quantify MRCCG patterns of STAD. The prognostic significance of MG Score was validated in three cohorts. The low MG score group, characterized by increased microsatellite instability-high (MSI-H), tumor mutation burden (TMB), PD-L1 expression, had a better prognosis. Interestingly, we demonstrated MRCCG patterns score could predict the sensitivity to ferroptosis inducing therapy. Our comprehensive analysis of MRCCGs in STAD demonstrated their potential roles in the tumor-immune-stromal microenvironment, clinicopathological features, and prognosis. Our findings highlight that MRCCGs may provide a new understanding of immunotherapy strategies for gastric cancer and provide a new perspective on the development of personalized immune therapeutic strategies for patients with STAD.

[Checkpoint inhibitors in colorectal carcinoma: are we entering a new era?]

BACKGROUND

Checkpoint-inhibitors have shown high response rates in some tumours such as melanomas.

OBJECTIVES

This article describes the data concerning the efficacy of checkpoint inhibitors in patients with colorectal cancer (CRC).

CURRENT DATA

Efficacy for the use of checkpoint inhibitors in CRC has only been shown for tumours with high microsatellite instability (MSI-H) or a deficient mismatch repair system (dMMR). The proportion of patients with MSI-H/dMMR cancers is 10-12% in colon cancers and 3% in rectal cancers. In cohort studies with patients that had progressed under at least one chemotherapy a response rate of 33% could be shown for pembrolizumab and 65% for the combination nivolumab and ipilimumab. In many patients the response was long-lasting. After 2 years between 55 and 75% of patients were still alive. In a randomized study comparing first-line therapy with pembrolizumab and chemotherapy progression-free survival was much longer for the pembrolizumab group (16.5 vs. 8.2 months). In a small series of patients with MSI-H/dMMR rectal cancers treatment with dostarlimab resulted in complete remission in all patients with no regrowth during an admittedly short follow-up. A series of patients with locally advanced MSI-H/dMMR colon cancers showed a treatment response in nearly all patients with 67% experiencing complete remission. In patients with microsatellite-stable (MSS) cancers checkpoint inhibitors showed no effect, the combination with chemotherapy at most a modest effect.

CONCLUSIONS

Checkpoint inhibitors are the first-choice palliative treatment in patients with MSI-H/dMMR CRC and have replaced chemotherapy as the first option. Early data show a high response rate for the neoadjuvant treatment of MSI-H/dMMR rectal and colon cancers.

Lung cancer presenting with central nervous system metastasis: Clinicopathological and molecular analysis of 171 cases

A subset of lung carcinoma presents initially with brain metastasis. Precise subtyping is mandatory for optimized treatment of these advanced aggressive carcinomas. We herein analyzed surgical biopsies from 171 Patients (99 males and 72 females aged 48-96; mean, 72), who presented with brain metastasis of lung cancer. In addition to conventional subtyping, we applied an extended immunohistochemistry (IHC) panel and performed several molecular tests looking for potential therapeutic targets other than EGFR mutations. Non-small cell carcinoma (NSCLC) comprised 157 (91.8 %) of cases: 109 (63.7 %) adenocarcinomas, 27 (15.8 %) squamous cell (SCC), 18 (10.5 %) large cell undifferentiated, 1 (0.6 %) adenosquamous and 2 (1.2 %) unclassified carcinomas. Of the adenocarcinomas, 81.7 % were TTF1+. Notably, 45 % of those TTF1-negative cases expressed HepPar1. SMARCA4 and SMARCA2 loss was observed in 13/171 (7.6 %) and 32/163 (19.6 %) cases, respectively; mainly TTF1- (40.0 %) and HepPar1+ (38.1 %) adenocarcinomas were affected by SMARCA2/4 loss. Loss of at least one mismatch repair (MMR) protein was observed in 3/156 (1.9 %) cases (2 adenocarcinomas and 1 large cell neuroendocrine carcinoma/LCNEC). Limited available data on mutation testing showed a frequency of EGFR mutations of 4.3% and of KRAS mutations of 57%. HER2 expression (2+/3+) was found in 45/166 (27.1 %) of cases with amplification verified by CISH in 18/38 (47.4 % of immunopositive cases and 10.5 % of the whole cohort); all but one were adenocarcinomas. Other genetic abnormalities detected included EML4::ALK rearrangements in 3 (1.8 %; 2 TTF1+ adenocarcinomas and 1 LCNEC) and RET rearrangements in one SCNEC. Variable subsets of tumors revealed amplifications of several potentially therapeutically targetable genes including MYC (30.0 %), MET (10.1 %), HER2 (10 %), FGFR1 (9.6 %), FGFR3 (4.6 %), and FGFR2 (3.4 %). This study highlights a highly heterogeneous molecular background in lung cancer presenting with CNS metastases. These findings highlight the need for individualized tumor testing strategies looking for potential therapeutic targets for this aggressive disease.

HER2+ endometrioid endometrial cancer possesses distinct molecular and immunologic features associated with a more active immune microenvironment and worse prognosis

OBJECTIVE

HER2 status is not routinely evaluated in endometrioid endometrial cancer (E-EMCA), though it is frequently overexpressed or amplified in high grade E-EMCA and uterine serous carcinoma. Defining characteristics and survival outcomes of HER2+ E-EMCA could reveal subsets of patients who may benefit from targeted therapies.

METHODS

2927 E-EMCA tumors from the Caris Life Sciences database were analyzed by next-generation sequencing and whole exome sequencing, whole transcriptome sequencing, and immunohistochemistry for molecular and genomic features in a CLIA/CAP-certified laboratory (Caris Life Sciences, Phoenix, AZ). HER2 status was determined by transcriptomic cutoff extrapolated from uterine serous carcinoma. The relationship between HER2 status and patient outcomes was determined by Kaplan-Meier analysis.

RESULTS

HER2 positivity was detected in 5.47% of E-EMCA. Differences in molecular alterations based on HER2 status were most apparent in microsatellite stable (MSS) tumors, which displayed increased TP53 mutations and loss of heterozygosity (LOH) and decreased PTEN and CTNNB1 mutations. HER2+ tumors had increased immune checkpoint gene expression and immune cell infiltration, particularly among MSS tumors. All HER2+ tumors displayed increased MAPK pathway activation scores (MPAS) and patients with HER2+ tumors experienced worse overall survival.

CONCLUSIONS

HER2 positivity in E-EMCA corresponds with a unique molecular landscape, particularly in MSS tumors. HER2+ tumors are also associated with increased MAPK pathway activation and exhibit features of a more active immune microenvironment. These findings suggest a potential benefit of HER2 and MAPK targeted therapies as well as immunotherapies in this patient population.

Diagnostic performance of Idylla MSI test in colorectal cancer biopsies

Universal testing for microsatellite instability (MSI) is recommended in colorectal cancer (CRC) to screen for Lynch syndrome and to guide optimal treatment and follow-up of the patients. Especially in neoadjuvant setting, where immuno-oncological treatments have recently shown excellent responses, identification of MSI status at biopsy is a prerequisite. Idylla MSI test offers a rapid and automated test to assess MSI-status from formalin-fixed paraffin-embedded tumor tissue sections. In this study, we compared the performance of the Idylla MSI test to mismatch repair (MMR) protein immunohistochemistry (IHC) using 117 CRC biopsies with previously known deficient MMR status. The concordance between Idylla and IHC was 99.0% (95/96) for biopsies with the recommended ≥ 20% tumor cell content. Further, 85.7% (18/21) of suboptimal CRC biopsy specimens (tumor cell content 5-15%) were diagnosed as MSI. Overall, we identified four discrepant cases of which three had tumor cell content less than 20%, explaining the discordant result. Our study shows that the Idylla MSI test offers a competent tool for MSI screening in CRC biopsy specimens.

Controlling the confounding effect of metabolic gene expression to identify actual metabolite targets in microsatellite instability cancers

BACKGROUND

The metabolome is the best representation of cancer phenotypes. Gene expression can be considered a confounding covariate affecting metabolite levels. Data integration across metabolomics and genomics to establish the biological relevance of cancer metabolism is challenging. This study aimed to eliminate the confounding effect of metabolic gene expression to reflect actual metabolite levels in microsatellite instability (MSI) cancers.

METHODS

In this study, we propose a new strategy using covariate-adjusted tensor classification in high dimensions (CATCH) models to integrate metabolite and metabolic gene expression data to classify MSI and microsatellite stability (MSS) cancers. We used datasets from the Cancer Cell Line Encyclopedia (CCLE) phase II project and treated metabolomic data as tensor predictors and data on gene expression of metabolic enzymes as confounding covariates.

RESULTS

The CATCH model performed well, with high accuracy (0.82), sensitivity (0.66), specificity (0.88), precision (0.65), and F1 score (0.65). Seven metabolite features adjusted for metabolic gene expression, namely, 3-phosphoglycerate, 6-phosphogluconate, cholesterol ester, lysophosphatidylethanolamine (LPE), phosphatidylcholine, reduced glutathione, and sarcosine, were found in MSI cancers. Only one metabolite, Hippurate, was present in MSS cancers. The gene expression of phosphofructokinase 1 (PFKP), which is involved in the glycolytic pathway, was related to 3-phosphoglycerate. ALDH4A1 and GPT2 were associated with sarcosine. LPE was associated with the expression of CHPT1, which is involved in lipid metabolism. The glycolysis, nucleotide, glutamate, and lipid metabolic pathways were enriched in MSI cancers.

CONCLUSIONS

We propose an effective CATCH model for predicting MSI cancer status. By controlling the confounding effect of metabolic gene expression, we identified cancer metabolic biomarkers and therapeutic targets. In addition, we provided the possible biology and genetics of MSI cancer metabolism.