Microsatellite instability in hereditary and sporadic breast cancers

Role of Surgical Pathologist for Detection of Predictive Immuno-oncological Factors in Breast Cancer

Immune checkpoint inhibitors (ICIs) have changed therapy strategies in breast cancer (BC) patients suffering from triple-negative breast cancer (TNBC). For example, in Europe the anti-programmed cell death 1 ligand 1 (PD-L1) ICI Azetolizumab is approved for adult patients with locally advanced or metastasized TNBC (mTNBC), depending on the immunohistochemical (IHC) PD-L1 expression of immune cells in the tumor area [immune cell (IC) score ≥1%); the anti-programmed cell death 1 (PD-1) ICI pembrolizumab is approved for mTNBC if PD-L1 Combined Positive Score (CPS), that is PD-L1 expression on tumor and/or immune cells, is ≥10. For early TNBC, in contrast, neoadjuvant use of pembrolizumab is approved in the United States and Europe independent from PD-L1 IHC expression. The determination of PD-L1 expression in tumor tissue to predict response to ICI therapy requires sensitive immunostaining with appropriate primary antibodies and staining protocols and a standardized and meticulous assessment of PD-L1 IHC stained breast cancer tissue slides. For the selection of the test material and continuous quality control of the dyeing, high standards must be applied. The evaluation is carried out according to various evaluation algorithms (scores). Here, the role of PD-L1 in BC and the currently most relevant PD-L1 assays and scores for TNBC will be explained. Furthermore, other tissue-based biomarkers potentially predictive for ICI therapy response in BC, for example, tumor mutational burden (TMB), will be presented in this review.

Looking beyond the cytogenetics in haematological malignancies: decoding the role of tandem repeats in DNA repair genes

BACKGROUND

In cancer research, one of the most significant findings was to characterize the DNA repair deficiency as carcinogenic. Amongst the various repair mechanisms, mismatch repair (MMR) and direct reversal of DNA damage systems are designated as multilevel safeguards in the human genome. Defects in these elevate the rate of mutations and results in dire consequences like cancer. Of the several molecular signatures in human genome, tandem repeats (TRs) appear at various frequencies in the exonic, intronic, and regulatory regions of the DNA. Hypervariability among these repeats in the coding and non-coding regions of the genes is well characterized for solid tumours, but its significance in haematologic malignancies remains to be explored. The purpose of our study was to elucidate the role of nucleotide repeat instability in the coding and non-coding regions of 10 different repair genes in myeloid and lymphoid cell lines compared to the control samples.

METHODS AND RESULTS

We selected MMR deficient extensively studied microsatellite instable colorectal cancer (HCT116), and MMR proficient breast cancer (MCF-7) cells along with underemphasized haematologic cancer cell lines to decipher the hypermutability of tandem repeats. A statistically significant TR variation was observed for MSH2 and MSH6 genes in 4 and 3 of the 6 cell lines respectively. KG1 (AML) and Daudi (Burkitt's lymphoma) were found to have compromised DNA repair competency with highly unstable nucleotide repeats.

CONCLUSION

Taken together, the results suggest that mutable TRs in intronic and non-intronic regions of repair genes in blood cancer might have a tumorigenic role. Since this is a pilot study on cell lines, high throughput research in large cohorts can be undertaken to reveal novel diagnostic markers for unexplained blood cancer patients with normal karyotypes or otherwise with karyotypic defects.

Tissue-agnostic drug approvals: how does this apply to patients with breast cancer?

Precision medicine has provided new perspectives in oncology, yielding research on the use of targeted therapies across different tumor types, regardless of their site of origin, a concept known as tissue-agnostic indication. Since 2017, the Food and Drug Administration (FDA) has approved the use of three different agents for tumor-agnostic treatment: pembrolizumab (for patients with microsatellite instability or high tumor mutational burden) and larotrectinib and entrectinib (both for use in patients harboring tumors with NTRK fusions). Importantly, the genomic alterations targeted by these agents are uncommon or rare in breast cancer, and little information exists regarding their efficacy in advanced breast cancer. In this review, we discuss the prevalence of these targets in breast cancer, their detection methods, the clinical characteristics of patients whose tumors have these alterations, and available data regarding the efficacy of these agents in breast cancer.

Mismatch Repair Deficiency Drives Durable Complete Remission by Targeting Programmed Death Receptor 1 in a Metastatic Luminal Breast Cancer Patient

BACKGROUND

In the field of breast cancer tumor biology, triple-negative breast cancer patients are the main focus of current clinical trials exploring the use of immune checkpoint inhibitors due to higher frequencies of somatic mutations, neoantigens, and resulting tumor-specific T-cell reactivity.

CASE REPORT

Here, we present the case of a 66-year-old woman with metastatic luminal breast cancer that rapidly responded to monotherapy with pembrolizumab, a monoclonal anti-PD-1 antibody. This patient obtained a partial clinical response within the first cycle of treatment and an ongoing durable complete remission after 12 weeks. Except for a transient immune-related thyreoiditis, there were no side effects observed offering remarkable quality of life to the patient. To evaluate the underlying mechanisms, we performed immunohistochemistry, explored the mutational landscape by whole-exome sequencing, and identified potential T-cell epitopes by prediction of neoantigens with high affinity binding to one of the patient's HLA. Briefly, we found a strong infiltration of CD8+ T cells without staining for PD-L1 in the tumor stroma. Exome sequencing revealed an enormous frequency of somatic and tumor-specific alterations, mainly C>T/G>A transitions. The mutational pattern was further linked to genome instability and deficient mismatch repair supported by the loss of MSH6 protein expression and therefore leading to susceptibility to immune checkpoint blockade.

CONCLUSION

Within the overall goal to establish operating procedures for breast cancer immunotherapy, we propose to re-evaluate testing for deficient mismatch repair and to further intensify the search for biomarkers predictive for the success of immune checkpoint modulation including all tumor biologic subtypes of breast cancer.

Clinicopathological features of breast cancer in Japanese female patients with Lynch syndrome

BACKGROUND

Lynch syndrome (LS) is a predominantly inherited syndrome caused by a pathological germline mutation in one of the mismatch repair (MMR) genes. Whether breast cancer (BC) is one of the LS-associated tumors is controversial. The aim of this retrospective cohort study was to evaluate the clinical features of BC in Japanese patients with LS.

METHODS

Of 38 mutation carriers, 4 females with BC were examined in this study.

RESULTS

Two of the four patients had multiple BC. Their median age at the diagnosis of BC was 63 (range, 47-84) years. The TNM (6th revision) stages of the six BCs were as follows: stage I, 33% (2/6); stage IIA, 50% (3/6); and stage IIB, 17% (1/6). Histological examination revealed four scirrhous, one papillotubular, and one medullary carcinoma. The positive ratios for estrogen receptor (ER), progesterone receptor (PgR), and human epidermal growth receptor 2 (HER2) were 83.3% (5/6), 83.3% (5/6), and 16.7% (1/6), respectively. Two of the three specimens showed MSI-H and one showed MSS. These MSI-H BCs had tumor-infiltrating lymphocytes. Two of the three specimens showed an absence of MLH1 and PMS2 proteins on immunohistochemistry. The cumulative risks for a person with LS to develop BC were 4.35% at the age of 50 years, 8.70% at 60 years, and 21.5% at 70 years.

CONCLUSIONS

Our study results showed BC in Japanese females with LS to be an MSI-H tumor, which was ER and PgR positive and HER2 negative.

The Importance of Distinguishing Sporadic Cancers from Those Related to Cancer Predisposing Germline Mutations

Choosing the optimal therapy for a patient's cancer has long been based on whether the cancer demonstrates a predictive marker of efficacy. The U.S. Food and Drug Administration (FDA) has now approved use of a targeted therapy based solely on tumor molecular markers (pembrolizumab for tumors with deficient mismatch repair [MMR] and high microsatellite instability [MSI]) and approved another therapy based solely on a germline mutation as the predictive marker of benefit (olaparib for BRCA carriers with ovarian or breast cancer) [New Engl J Med 2017;377:1409-1412, N Engl J Med 2012;366:1382-1392, N Eng J Med 2017;377:523-533].Here, a patient is presented with a molecular diagnosis of Lynch syndrome and with breast cancer. Yet the breast cancer showed proficient expression of the same MMR gene found to be mutated in her germline testing. The case underscores the importance of tumor testing for MMR and MSI and of not assuming that the tumor is related to the Lynch syndrome rather than being sporadic. This is particularly true in patients with cancers (e.g., breast cancer) whose association with Lynch syndrome is not well established.The case presented also underscores the importance of considering next-generation sequencing of the tumor when the therapies approved are based on a germline mutation being the predictive marker. For example, the FDA-approved use of the PARP inhibitor olaparib is for ovarian or breast cancers in patients harboring a BRCA germline mutation [N Engl J Med 2012;366:1382-1392, N Eng J Med 2017;377:523-533]. Yet patients with tumors lacking BRCA loss of heterozygosity (LOH) or lacking other evidence of probable loss of normal BRCA gene product expression might be less likely to benefit from PARP inhibitor therapy, because the efficacy of PARP inhibitor therapy in patients with germline BRCA mutations would likely be predicated upon BRCA LOH in their tumors. KEY POINTS: Cancers in patients with germline mutations may be sporadic and unrelated to the germline mutation.Lynch syndrome is due to a germline mutated mismatch repair (MMR) gene. Cancers resulting from the germline MMR gene mutation as the predisposing event would be expected to be MMR deficient (dMMR) and microsatellite instability high (MSI-H). Sporadic cancers in patients with Lynch syndrome would be expected to be MMR proficient or microsatellite stable.Pembrolizumab is only approved for solid tumors demonstrating dMMR/MSI-H. Thus, whether the cancer tissue of origin is clearly associated with Lynch syndrome or not yet clearly established as a Lynch syndrome-related cancer (e.g., breast cancer), establishing the tumor to be dMMR/MSI-H is necessary to predict possible benefit and endorse the use of pembrolizumab.Ovarian cancers that develop in BRCA germline mutation carriers are so often related to the inherited mutated BRCA as the predisposing factor that testing the tumor for the footprint of BRCA-related ovarian cancer (BRCA loss of heterozygosity) is not necessary for use of the PARP inhibitor therapy olaparib. Future studies that include tumor evaluation for normal BRCA expression or surrogates of normal BRCA gene product expression might help determine which patients harboring a germline BRCA mutation are most likely to benefit from PARP inhibitor therapy.

Checkpoint Inhibitors in the Treatment of Breast Cancer

PURPOSE OF REVIEW

The treatment landscape for many cancers has dramatically changed with the development of checkpoint inhibitors. This article will review the literature concerning the use of checkpoint inhibitors in breast cancer.

RECENT FINDINGS

The histological subtype of BC with the strongest signal of efficacy has been triple-negative breast cancer (TNBC). Early trials of single-agent checkpoint inhibitors did not demonstrate a uniformly positive signal. Clinical studies suggest response rates between 5 and 10% in pretreated patients and roughly 20-25% for untreated advanced TNBC. However, in the small subset of patients who do respond, the response is often durable. More encouraging results have been reported with their use in combination with chemotherapy in the neoadjuvant setting. Larger phase III studies are underway to confirm these earlier findings. An immune-directed therapeutic approach for the management of BC is underway, and it is likely that combination therapy will be required to achieve a level of efficacy worthy of use in the BC treatment paradigm. These agents are not without both economic and clinical toxicity; therefore, it is imperative that we identify patients most likely to benefit from these therapies through well-designed biologically plausible clinical studies and by evaluating novel combinatorial approaches with informative biomarker driven correlative studies.

Hypermutated tumours in the era of immunotherapy: The paradigm of personalised medicine

Immune checkpoint inhibitors have demonstrated unprecedented clinical activity in a wide range of cancers. Significant therapeutic responses have recently been observed in patients presenting mismatch repair-deficient (MMRD) tumours. MMRD cancers exhibit a remarkably high rate of mutations, which can result in the formation of neoantigens, hypothesised to enhance the antitumour immune response. In addition to MMRD tumours, cancers mutated in the exonuclease domain of the catalytic subunit of the DNA polymerase epsilon (POLE) also exhibit an ultramutated genome and are thus likely to benefit from immunotherapy. In this review, we provide an overview of recent data on hypermutated tumours, including MMRD and POLE-mutated cancers, with a focus on their distinctive clinicopathological and molecular characteristics as well as their immune environment. We also discuss the emergence of immune therapy to treat these hypermutated cancers, and we comment on the recent Food and Drug Administration approval of an immune checkpoint inhibitor, the programmed cell death 1 antibody (pembrolizumab, Keytruda), for the treatment of patients with metastatic MMRD cancers regardless of the tumour type. This breakthrough represents a turning point in the management of these hypermutated tumours and paves the way for broader strategies in immunoprecision medicine.

Investigation of Cross-Contamination and Misidentification of 278 Widely Used Tumor Cell Lines

In recent years, biological research involving human cell lines has been rapidly developing in China. However, some of the cell lines are not authenticated before use. Therefore, misidentified and/or cross-contaminated cell lines are unfortunately commonplace. In this study, we present a comprehensive investigation of cross-contamination and misidentification for a panel of 278 cell lines from 28 institutes in China by using short tandem repeat profiling method. By comparing the DNA profiles with the cell bank databases of ATCC and DSMZ, a total of 46.0% (128/278) cases with cross-contamination/misidentification were uncovered coming from 22 institutes. Notably, 73.2% (52 out of 71) of the cell lines established by the Chinese researchers were misidentified and accounted for 40.6% of total misidentification (52/128). Further, 67.3% (35/52) of the misidentified cell lines established in laboratories of China were HeLa cells or a possible hybrid of HeLa with another kind of cell line. Furthermore, the bile duct cancer cell line HCCC-9810 and degenerative lung cancer Calu-6 exhibited 88.9% match in the ATCC database (9-loci), indicating that they were from the same origin. However, when we used 21-loci to compare these two cell lines with the same algorithm, the percent match was only 48.2%, indicating that these two cell lines were different. The SNP profiles of HCCC-9810 and Calu-6 also revealed that they were different cell lines. 150 cell lines with unique profiles demonstrated a wide range of in vitro phenotypes. This panel of 150 genomically validated cancer cell lines represents a valuable resource for the cancer research community and will advance our understanding of the disease by providing a standard reference for cell lines that can be used for biological as well as preclinical studies.

Microsatellite Instability as a Biomarker for PD-1 Blockade

Initial results by Le and colleagues, which were published in the June 25, 2015 issue of the New England Journal of Medicine, report significant responses of cancers with microsatellite instability (MSI) to anti-PD-1 inhibitors in patients who failed conventional therapy. This finding fits into a broader body of research associating somatic hypermutation and neoepitope formation with response to immunotherapy, with the added benefit of relying on a simple, widely used diagnostic test. This review surveys the pathogenesis and prognostic value of MSI, diagnostic guidelines for detecting it, and the frequency of MSI across tumors, with the goal of providing a reference for its use as a biomarker for PD-1 blockade. MSI usually arises from either germline mutations in components of the mismatch repair (MMR) machinery (MSH2, MSH6, MLH1, PMS2) in patients with Lynch syndrome or somatic hypermethylation of the MLH1 promoter. The result is a cancer with a 10- to 100-fold increase in mutations, associated in the colon with poor differentiation, an intense lymphocytic infiltrate, and a superior prognosis. Diagnostic approaches have evolved since the early 1990s, from relying exclusively on clinical criteria to incorporating pathologic features, PCR-based MSI testing, and immunohistochemistry for loss of MMR component expression. Tumor types can be grouped into categories based on the frequency of MSI, from colorectal (20%) and endometrial (22%-33%) to cervical (8%) and esophageal (7%) to skin and breast cancers (0%-2%). If initial results are validated, MSI testing could have an expanded role as a tool in the armamentarium of precision medicine.

Genomic Changes in Normal Breast Tissue in Women at Normal Risk or at High Risk for Breast Cancer

Sporadic breast cancer develops through the accumulation of molecular abnormalities in normal breast tissue, resulting from exposure to estrogens and other carcinogens beginning at adolescence and continuing throughout life. These molecular changes may take a variety of forms, including numerical and structural chromosomal abnormalities, epigenetic changes, and gene expression alterations. To characterize these abnormalities, a review of the literature has been conducted to define the molecular changes in each of the above major genomic categories in normal breast tissue considered to be either at normal risk or at high risk for sporadic breast cancer. This review indicates that normal risk breast tissues (such as reduction mammoplasty) contain evidence of early breast carcinogenesis including loss of heterozygosity, DNA methylation of tumor suppressor and other genes, and telomere shortening. In normal tissues at high risk for breast cancer (such as normal breast tissue adjacent to breast cancer or the contralateral breast), these changes persist, and are increased and accompanied by aneuploidy, increased genomic instability, a wide range of gene expression differences, development of large cancerized fields, and increased proliferation. These changes are consistent with early and long-standing exposure to carcinogens, especially estrogens. A model for the breast carcinogenic pathway in normal risk and high-risk breast tissues is proposed. These findings should clarify our understanding of breast carcinogenesis in normal breast tissue and promote development of improved methods for risk assessment and breast cancer prevention in women.

Mismatch Repair Deficiency and Response to Immune Checkpoint Blockade

: More than 1.6 million new cases of cancer will be diagnosed in the U.S. in 2016, resulting in more than 500,000 deaths. Although chemotherapy has been the mainstay of treatment in advanced cancers, immunotherapy development, particularly with PD-1 inhibitors, has changed the face of treatment for a number of tumor types. One example is the subset of tumors characterized by mismatch repair deficiency and microsatellite instability that are highly sensitive to PD-1 blockade. Hereditary forms of cancer have been noted for more than a century, but the molecular changes underlying mismatch repair-deficient tumors and subsequent microsatellite unstable tumors was not known until the early 1990s. In this review article, we discuss the history and pathophysiology of mismatch repair, the process of testing for mismatch repair deficiency and microsatellite instability, and the role of immunotherapy in this subset of cancers.

IMPLICATIONS FOR PRACTICE

Mismatch repair deficiency has contributed to our understanding of carcinogenesis for the past 2 decades and now identifies a subgroup of traditionally chemotherapy-insensitive solid tumors as sensitive to PD-1 blockade. This article seeks to educate oncologists regarding the nature of mismatch repair deficiency, its impact in multiple tumor types, and its implications for predicting the responsiveness of solid tumors to immune checkpoint blockade.

Mismatch Repair Deficiency and Response to Immune Checkpoint Blockade

: More than 1.6 million new cases of cancer will be diagnosed in the U.S. in 2016, resulting in more than 500,000 deaths. Although chemotherapy has been the mainstay of treatment in advanced cancers, immunotherapy development, particularly with PD-1 inhibitors, has changed the face of treatment for a number of tumor types. One example is the subset of tumors characterized by mismatch repair deficiency and microsatellite instability that are highly sensitive to PD-1 blockade. Hereditary forms of cancer have been noted for more than a century, but the molecular changes underlying mismatch repair-deficient tumors and subsequent microsatellite unstable tumors was not known until the early 1990s. In this review article, we discuss the history and pathophysiology of mismatch repair, the process of testing for mismatch repair deficiency and microsatellite instability, and the role of immunotherapy in this subset of cancers.

IMPLICATIONS FOR PRACTICE

Mismatch repair deficiency has contributed to our understanding of carcinogenesis for the past 2 decades and now identifies a subgroup of traditionally chemotherapy-insensitive solid tumors as sensitive to PD-1 blockade. This article seeks to educate oncologists regarding the nature of mismatch repair deficiency, its impact in multiple tumor types, and its implications for predicting the responsiveness of solid tumors to immune checkpoint blockade.

Somatic microsatellite variability as a predictive marker for colorectal cancer and liver cancer progression

Microsatellites (MSTs) are short tandem repeated genetic motifs that comprise ~3% of the genome. MST instability (MSI), defined as acquired/lost primary alleles at a small subset of microsatellite loci (e.g. Bethesda markers), is a clinically relevant marker for colorectal cancer. However, these markers are not applicable to other types of cancers, specifically, for liver cancer which has a high mortality rate. Here we show that somatic MST variability (SMV), defined as the presence of additional, non-primary (aka minor) alleles at MST loci, is a complementary measure of MSI, and a genetic marker for colorectal and liver cancer. Re-analysis of Illumina sequenced exomes from The Cancer Genome Atlas indicates that SMV may distinguish a subpopulation of African American patients with colorectal cancer, which represents ~33% of the population in this study. Further, for liver cancer, a higher rate of SMV may be indicative of an earlier age of onset. The work presented here suggests that classical MSI should be expanded to include SMV, going beyond alterations of the primary alleles at a small number of microsatellite loci. This measure of SMV may represent a potential new diagnostic for a variety of cancers and may provide new information for colorectal cancer patients.

Oncogene-triggered suppression of DNA repair leads to DNA instability in cancer

DNA instability is an important contributor to cancer development. Previously, defects in the chromosome segregation and excessive DNA double strand breaks due to the replication or oxidative stresses were implicated in DNA instability in cancer. Here, we demonstrate that DNA instability can directly result from the oncogene-induced senescence signaling. Expression of the activated form of Her2 oncogene, NeuT, in immortalized breast epithelial cells led to downregulation of the major DNA repair factor histone H2AX and a number of other components of the HR and NHEJ double strand DNA breaks repair pathways. H2AX expression was regulated at the transcriptional level via a senescence pathway involving p21-mediated regulation of CDK and Rb1. The p21-dependent downregulation of H2AX was seen both in cell culture and the MMTV-neu mouse model of Her2-positive breast cancer. Importantly, downregulation of H2AX upon Her2/NeuT expression impaired repair of double strand DNA breaks. This impairment resulted in both increased DNA instability in the form of somatic copy number alterations, and in increased sensitivity to the chemotherapeutic drug doxorubicin. Overall, these findings indicate that the Her2/NeuT oncogene signaling directly potentiates DNA instability and increases sensitivity to DNA damaging treatments.

The molecular background of mucinous carcinoma beyond MUC2

The increasing interest of the oncology community in tumour classification and prediction of outcome to targeted therapies has put emphasis on an improved identification of tumour types. Colorectal mucinous adenocarcinoma (MC) is a subtype that is characterized by the presence of abundant extracellular mucin that comprises at least 50% of the tumour volume and is found in 10–15% of colorectal cancer patients. MC development is poorly understood, however, the distinct clinical and pathological presentation of MC suggests a deviant development and molecular background. In this review we identify common molecular and genetic alterations in colorectal MC. MC is characterized by a high rate of MUC2 expression. Mutation rates in the therapeutically important RAS/RAF/MAPK and PI3K/AKT pathways are significantly higher in MC compared with non‐mucinous adenocarcinoma. Furthermore, mucinous adenocarcinoma shows higher rates of microsatellite instability and is more frequently of the CpG island methylator phenotype. Although the majority of MCs arise from the large intestine, this subtype also develops in other organs, such as the stomach, pancreas, biliary tract, ovary, breast and lung. We compared findings from colorectal MC with tumour characteristics of MCs from other organs. In these organs, MCs show different mutation rates in the RAS/RAF/MAPK and PI3K/AKT pathways as well, but a common mucinous pathway cannot be identified. Identification of conditions and molecular aberrations that are associated with MC generates insight into the aetiology of this subtype and improves understanding of resistance to therapies.

DNA mismatch repair deficiency in breast carcinoma: a pilot study of triple-negative and non-triple-negative tumors

Recent studies have suggested that breast cancer is part of the tumor spectrum in Lynch syndrome (LS). However, the frequency and significance of DNA mismatch repair (MMR) deficiency in breast carcinoma in general is unclear. Some triple-negative breast carcinomas (TNBCs) have morphologic features similar to those described in LS-associated colorectal carcinomas; therefore, we hypothesized that TNBCs might be more likely to have MMR deficiency. In this study, we tested our hypothesis in a series of 226 TNBCs along with a control series of 90 non-triple-negative tumors, utilizing DNA MMR protein immunohistochemistry followed by PCR microsatellite instability testing and MLH1 promoter methylation testing. By immunohistochemistry, we identified 4 triple-negative carcinomas (4/226, 1.8%) showing loss of MMR proteins (3 lost MLH1 and PMS2, and 1 lost MSH2 and MSH6); whereas none of the 90 non-triple-negative carcinomas showed loss of protein. Further testing of the 3 MLH1/PMS2 protein-deficient carcinomas identified 1 tumor showing high-frequency microsatellite instability and MLH1 promoter hypermethylation. All 4 MMR protein-deficient carcinomas were ductal type with high histologic and nuclear grades. Prominent lymphocytic infiltration was noted in 2 tumors. The clinical characteristics and survival outcome varied widely among the 4 patients. In conclusion, our results suggest that DNA MMR deficiency is rare in breast carcinoma, and as such, testing of breast carcinoma for the detection of LS may best be restricted to high-risk individuals only. Our data also suggest that not all MMR protein-deficient breast tumors show microsatellite instability, and MLH1 promoter methylation is the molecular basis for at least a subset of microsatellite instable breast tumors. Although MMR-deficient breast carcinomas share certain morphologic features with the more typical types of LS-associated tumors, better characterization, and a better understanding of their clinical behavior await further analysis with a larger sample size.

Is breast cancer a part of Lynch syndrome?

A long-standing question is whether breast cancer is an integral part of Lynch syndrome, also known as hereditary non-polyposis colorectal cancer. A recent study by Lotsari and colleagues analyzes molecular features of breast cancers from families with Lynch syndrome, including germline mutation carriers and their non-mutation carrier siblings, and controls with sporadic breast cancer. The study finds microsatellite instability and loss of mismatch DNA repair protein expression in one third and two thirds of Lynch syndrome samples, respectively, but in none of the non-mutation carriers or controls. Overall, the age of diagnosis of breast cancer in Lynch syndrome mutation carriers is no different than that in non-carriers, but diagnosis age was lower in those carriers whose breast tumors exhibited defects in mismatch repair. These results have important implications for genetic counseling and genetic testing of families with breast cancer and other tumors associated with Lynch syndrome, such as colorectal and endometrial cancers.

Breast carcinoma and Lynch syndrome: molecular analysis of tumors arising in mutation carriers, non-carriers, and sporadic cases

Introduction

Breast carcinoma is the most common cancer in women, but its incidence is not increased in Lynch syndrome (LS) and studies on DNA mismatch repair deficiency (MMR) in LS-associated breast cancers have arrived at conflicting results. This study aimed to settle the question as to whether breast carcinoma belongs to the LS tumor spectrum.

Methods

MMR status and epigenetic profiles were determined for all available breast carcinomas identified among 200 LS families from a nation-wide registry (23 tumors from mutation carriers and 18 from non-carriers). Sporadic breast carcinomas (n = 49) and other cancers (n = 105) from MMR gene mutation carriers were studied for comparison.

Results

The proportion of breast carcinomas that were MMR-deficient based on absent MMR protein, presence of microsatellite instability, or both was significantly (P = 0.00016) higher among breast carcinomas from mutation carriers (13/20, 65%) compared to non-carriers (0/14, 0%). While the average age at breast carcinoma diagnosis was similar in carriers (56 years) and non-carriers (54 years), it was lower for MMR-deficient versus proficient tumors in mutation carriers (53 years versus 61 years, P = 0.027). Among mutation carriers, absent MMR protein was less frequent in breast carcinoma (65%) than in any of seven other tumor types studied (75% to 100%). Tumor suppressor promoter methylation patterns were organ-specific and similar between breast carcinomas from mutation carriers and non-carriers.

Conclusions

Breast carcinoma from MMR gene mutation carriers resembles common breast carcinoma in many respects (for example, general clinicopathological and epigenetic profiles). MMR status makes a distinction: over half are MMR-deficient typical of LS spectrum tumors, while the remaining subset which is MMR-proficient may develop differently. The results are important for appropriate surveillance in mutation carriers and may be relevant for LS diagnosis in selected cases.

Evidence for breast cancer as an integral part of Lynch syndrome

Lynch syndrome, an autosomal dominant cancer predisposition caused by mutations in DNA mismatch repair (MMR) genes, mainly mainly mutL homolog 1, OMIM 120436 (MLH1) and mutS homolog 2, OMIM 609309 (MSH2), encompasses a tumor spectrum including primarily gastrointestinal, endometrial, and ovarian cancer. This study aimed at clarifying the heavily debated issue of breast cancer being part of Lynch syndrome. Detailed clinical data on cancer occurrence in Swiss female MLH1/MSH2 mutation carriers were gathered, all available breast cancer specimens assessed for molecular evidence for MMR deficiency (i.e., microsatellite instability (MSI), MMR protein expression, and somatic (epi)genetic MMR gene alterations) and compiled with the scarce molecular data available from the literature. Seventy unrelated Swiss Lynch syndrome families were investigated comprising 632 female family members at risk of which 92 were genetically verified mutation carriers (52 MLH1 and 40 MSH2). On contrast to endometrial and ovarian cancer, which occurred significantly more often and at younger age in MLH1/MSH2 mutation carriers (median 50.5 and 49.0 years; P < 0.00001), overall cumulative breast cancer incidence closely mirrored the one in the Swiss population (56.5 years). Six (85.7%) of seven breast cancer specimens available for molecular investigations displayed the hallmarks of MMR deficiency. Combined with data from the literature, MSI was present in 26 (70.3%) of 37 and altered MMR protein expression in 16 (72.7%) of 22 breast cancer specimens from MLH1/MSH2 mutation carriers. These findings, thus, provide strong molecular evidence for a pivotal role of MMR deficiency in breast cancer development in Lynch syndrome.

Phenotype-genotype correlation in familial breast cancer

Familial breast cancer accounts for a small but significant proportion of breast cancer cases worldwide. Identification of the candidate genes is always challenging specifically in patients with little or no family history. Therefore, a multidisciplinary team is required for the proper detection and further management of these patients. Pathologists have played a pivotal role in the cataloguing of genotypic-phenotypic correlations in families with hereditary cancer syndromes. These efforts have led to the identification of histological and phenotypic characteristics that can help predict the presence or absence of germline mutations of specific cancer predisposition genes. However, the panoply of cancer phenotypes associated with mutations of genes other than in BRCA1 is yet to be fully characterised; in fact, many cancer syndromes, germline mutations and gene sequence variants are under investigation for their possible morphological associations. Here we review the current understanding of phenotype-genotype correlation in familial breast cancer.

Systemic chemotherapy-induced microsatellite instability in the mononuclear cell fraction of women with breast cancer can be reproduced in vitro and abrogated by amifostine

OBJECTIVES

Microsatellite instability (MSI) induction by alkylating agent-based chemotherapy (ACHT) may underlie both tumor resistance to chemotherapy and secondary leukaemias in cancer patients. We investigated if ACHT could induce MSI in tumor-derived plasma-circulating DNA (pfDNA) and in normal peripheral blood mononuclear (PBMN) cells. We also evaluated if amifostine could interfere with this process in an in-vitro model.

METHODS

MSI was determined in pfDNA, PBMN cells and urine cell-free DNA (ufDNA) of 33 breast cancer patients before and after ACHT. MCF-7 cells and PBMN from normal donors were exposed in vitro to melphalan, with or without amifostine.

RESULTS

We observed at least one MSI event in PBMN cells, pfDNA or ufDNA of 87, 80 and 80% of patients, respectively. In vitro, melphalan induced MSI in both MCF-7 and normal PBMN cells. In PBMN cells, ACHT-induced MSI occurred together with a significant decrease in the expression of the DNA mismatch repair gene hMSH2. Amifostine decreased hMSH2 expression and also prevented MSI induction only in normal PBMN cells.

CONCLUSIONS

ACHT induced MSI in PBMN cells and in tumour-derived pfDNA. Because of its protective effect against ACHT induction of MSI in normal PBMN cells in vitro, amifostine may be a potential agent for preventing secondary leukaemias in patients exposed to ACHT.

Mismatch repair genes hMLH1 and hMSH2 may not play an essential role in breast carcinogenesis

Breast carcinoma is one of the most common malignancies in women, and its carcinogenesis is still unknown. The role of microsatellite instability (MSI) in breast carcinogenesis has been inconsistent in the literature. Here we studied the expression of 2 mismatch repair genes, hMLH1 and hMSH2, in 211 cases of intraductal (DCIS; 90 cases) and invasive ductal carcinoma (121 cases) of the breast by immunohistochemical analysis; and evaluated its relationship with cytokeratin (CK) subtypes, along with expression of ER-alpha (138 cases positive, 73 cases negative); PR (118 cases positive, 93 cases negative), and HER-2/neu (47 cases positive, 164 cases negative); and clinical features such as patient age (157 cases>50 years, 54 cases<50 years), tumor size (31 cases of IDC>2 cm, 90 cases of IDC<2 cm), tumor grade (87 cases high nuclear grade, 124 case non-high grade), and lymph node metastasis (38 cases of IDC positive, 74 cases of IDC negative, 9 cases of IDC with no available data on lymph node status). For CK subtypes, 167 cases were classified as luminal subtype (expressing CK8 and/or CK18, negative for CK5/6, CK14, and CK17) and 44 cases were classified as nonluminal (most of them belonged to basal/stem subtype, expressing CK5/6, and/or CK14, and/or CK17). No typical or atypical medullary carcinoma was included in this study. Our results showed that no loss of nuclear expression of either hMLH1 or hMSH2 was identified in any of the 211 cases of DCIS or IDC regardless of the various pathological and clinical factors, suggesting that hMLH1 or hMSH2 may not play an essential role in the majority of cases of the breast carcinoma.

Microsatellite instability in Ewing tumor is not associated with loss of mismatch repair protein expression

Only few clinical factors predict the prognosis of patients with Ewing tumors. Unfavorable outcome is associated with primary metastatic disease, age > 15 years, tumor volume above 200 ml, and the histological response to chemotherapy. The aim of this study was to elucidate the prevalence and clinical impact of microsatellite instability (MSI) together with the relation between MSI and mismatch repair protein expression in Ewing tumors. DNA from 61 primary Ewing tumors and 11 Ewing tumor cell lines was extracted and microsatellite analysis for the detection of instability or loss of heterozygosity was performed for the five markers of the Bethesda panel BAT25, BAT26, D5S346, D2S123, and D17S250, which represents the established marker panel for the analysis of hereditary non-polyposis colorectal carcinoma (HNPCC) patients. In addition, single nucleotide repeat regions of the two tumor genes BAX and transforming growth factor receptor II (TGFBR2) were also included. All of the 61 samples were suitable for LOH analysis and 55 for the determination of MSI-status. LOH of these microsatellite markers was detected in 9 of the 61 patients (14.8%). Over all, genetic instability, i.e. MSI and/or LOH, was detected in 17 tumors (27.9%). One out of the 11 tumor cell lines (STA ET1) was characterized by instability of all the five Bethesda markers, while from primary tumor samples, only one showed MSI in more than one microsatellite marker (D5S346 and D17S250, MSI-high). Eight of the fifty-five patients (14.5%) showed instability of one microsatellite locus (MSI-low). No instability was detected in BAT26, D2S123, BAX and TGFBR2. There was no significant correlation between MSI and loss of expression of mismatch repair proteins MLH1, MSH2, or MSH6. The impairment of the p53 signaling pathway (expression of TP53 and/or MDM2 by immunohistochemistry) was significantly associated with reduced overall survival (15 of 49 patients (30.6%), P = 0.0410, log-rank test). We conclude that MSI is not prevalent in Ewing tumor and that the nature of instability differs from the form observed in colorectal carcinoma, the model tumor of MSI. This is documented by the different pattern of MSI (no BAT26 instability) in Ewing tumors and the lack of a strict correlation between MSI-high and loss of expression of MSH2, MSH6 and MLH1.

DNA Methylation Profiles of Female Steroid Hormone-Driven Human Malignancies

Tumor DNA contains valuable clues about the origin and pathogenesis of human cancers. Alterations in DNA methylation can lead to silencing of genes associated with distinct tumorigenic pathways. These pathway-specific DNA methylation changes help define tumor-specific DNA methylation profiles that can be used to further our understanding of tumor development, as well as provide tools for molecular diagnosis and early detection of cancer. Female sex hormones have been implicated in the etiology of several of the women's cancers including breast, endometrial, ovarian, and proximal colon cancers. We have reviewed the DNA methylation profiles of these cancers to determine whether the hormonal regulation of these cancers results in specific DNA methylation alterations. Although subsets of tumors in each of these four types of cancers were found to share some DNA methylation alterations, we did not find evidence for global hormone-specific DNA methylation alterations, suggesting that female sex hormones may participate in different tumorigenic pathways that are associated with distinct DNA methylation-based molecular signatures. One such pathway may include MLH1 methylation in the context of the CpG island methylator phenotype.

Microsatellite instability analysis of bilateral breast tumors suggests treatment-related origin of some contralateral malignancies

PURPOSE

High-frequency microsatellite instability (MSI-H) occurs frequently in colorectal cancers and some other tumor types, but is very uncommon in breast cancer. In the earlier study devoted to microsatellite analysis of allelic imbalances, the authors accidentally detected several MSI-H tumors in patients with the bilateral form of breast cancer (biBC). The present study was designed to examine this unexpected phenomenon in more detail.

METHODS

All DNA samples were tested by the standard panel of MSI-specific markers BAT25, BAT26, BAT40, D5S346, and D17S250. If the tumor was unstable for at least one marker, or PCR amplification was not successful for any of the listed above loci, the analysis of additional five dinucleotide markers (D1S225, D11S4167, D22S272, D22S1166, and D3S3527) was performed. Tumors showing instability in > or = 30% loci were classified as MSI-H.

RESULTS

In biBC group, MSI-H status was detected in 6/60 (10%) contralateral tumors, but in 0/50 (0%) first malignancies (P = 0.021) and only in 1/22 (5%) synchronous biBC (P = 0.434). None of 52 unilateral breast cancers showed MSI-H status. Shifts of mononucleotide markers were revealed in four second carcinomas from biBC patients but in none of the breast tumors from other categories.

CONCLUSIONS

MSI-H is detected with a noticeable frequency in bilateral but not in unilateral breast cancers. Preferable occurrence of MSI-H in second metachronous tumors from biBC patients allows to hypothesize that the development of some contralateral breast neoplasms is casually related to the adjuvant treatment of the initial malignancy.

DNA hypermethylation in breast cancer and its association with clinicopathological features

Aberrant hypermethylation of gene promoter regions is one of the mechanisms for inactivation of tumour suppressor genes in breast cancer. We investigated whether hypermethylation identifies breast cancers with distinctive clinical and pathological features. We evaluated the methylation of RARbeta2, CDH1, ER, BRCA1, CCND2, p16 and TWIST in 193 breast carcinomas. Methylation frequencies ranged from 11% for CCND2 to 84% for ER. Tumours with frequent methylation (4-6 genes) were more often poorly differentiated compared to those with infrequent methylation (0-2 genes; P=0.004). Tumours with ER and CDH1 methylation were associated with significantly lower hormone receptor levels, younger age at diagnosis and the presence of mutant p53. Our data suggests that gene methylation may be linked to various pathological features of breast cancer, however, this requires confirmation in larger studies.

Anti-apoptotic proteins induce non-random genetic alterations that result in selecting breast cancer metastatic cells

To shed light on the relationships between over-expression of anti-apoptotic proteins, genomic instability, and the metastatic ability of breast cancer cells, we analyzed genetic changes in tumors and metastases by orthotopically injecting MDA-MB 435 cells transfected with anti-apoptotic genes Bcl-xL or Bcl-2 into nude mice. Tumors and metastasis variants were extracted by primary culture from breast, bone, lung, and lymph node from mice with 435/Bcl-xL, 435/Bcl-2, and 435/Neo tumors. Using the Arbitrarily Primed Polymerase Chain Reaction (AP-PCR), which permits the detection of allelic imbalances, we generated four different fingerprints utilizing four primers. We found that the genetic damage fraction (GDF) increased in 435/Bcl-2 (GDF=0.55) and 435/Bcl-xL cells (GDF=0.34), in regard to 435/Neo control cells (GDF=0.29), indicating that non-random genetic alterations occurred in cells secondary to Bcl-2 or Bcl-xL over-expression. Anti-apoptotic proteins render breast cancer cells susceptible to the in vivo acquisition of highly tumorigenic (Kruskal-Wallis, P=0.019) and metastatic (Kruskal-Wallis, P=0.004) activity. We therefore propose that genetic instability is a molecular mechanism favored by anti-apoptotic proteins involved in the selection of highly metastatic cells during tumorigenesis, a pathogenic event favoring the expansion of metastasis.

Right- and left-sided colorectal cancers display distinct expression profiles and the anatomical stratification allows a high accuracy prediction of lymph node metastasis

Accurate preoperative prediction of lymph node metastasis and degree of tumor invasion would facilitate an appropriate decision of the extent of surgical resection of cancers to reduce unnecessary complication or to minimize the risk of recurrence in patients. We analyzed gene expression profiles characteristic of the invasiveness of colorectal carcinoma in a total of 89 cases, using a cDNA array and pattern classification algorithms. We set binary classes for a panel of clinicopathologic parameters, each of which was divided at different levels for categories (discrete) or values (continuous). We searched an optimal combination of genes to discriminate the classes by using of a feature subset selection algorithm, which was applied to a set of genes preselected on the basis of statistical difference in expression (two-sided t test, P < or = 0.05). We used a sequential forward feature selection which additively searched a combination of genes, giving a minimal leave-one-out classification error rate of a k-nearest neighbor classifier. In the process of gene preselection, we found a remarkable difference in the expression pattern of genes according to the anatomical location of cancers. The difference was most prominent when the classes were set for cecum, ascending colon, transverse colon, and descending colon (CATD) versus sigmoid colon and rectum (SR). By stratifying these two locations, we were able to extract gene expression profiles characteristic of the classes of the presence versus absence of lymph node metastasis, lymphatic invasion, vascular invasion and degree of mural invasion, and pathological stages, with an accuracy of more than 90%. These results suggest that colorectal cancers harbor distinct molecular pathophysiological statuses according to their right-to-left locations, of which stratification is important for pattern classification of cDNA array data.

Telomere shortening occurs early during breast tumorigenesis: a cause of chromosome destabilization underlying malignant transformation?

Chromosomal instability appears early during breast carcinogenesis and is considered a major driving force in malignant transformation. While current evidence suggests that centrosomal and mitotic checkpoint defects may, in large part, account for numerical chromosomal abnormalities, the mechanisms underlying structural chromosomal abnormalities remain largely unknown. Telomeres stabilize and protect chromosomal termini, but shorten due to cell division and oxidative damage. Moderate telomere shortening signals a tumor suppressive growth arrest in normal cells. Critically short telomeres, in the setting of abrogated DNA damage checkpoints, cause chromosomal instability due to end-to-end chromosomal fusions, subsequent breakage, and rearrangement, resulting in an increased cancer incidence in animal models. Recent results from high resolution in situ telomere length assessment in human breast tissues indicate that significant telomere shortening is prevalent in preinvasive breast lesions (DCIS), as well as focal areas of histologically normal epithelium from which breast carcinoma is thought to arise. Telomere shortening is therefore a strong candidate for the cause of structural chromosome defects that contribute to breast cancer development.