Microsatellite instability in in situ and invasive sporadic breast cancers of Japanese women

Microsatellite instability in Japanese female patients with triple-negative breast cancer

Background

It is important to identify biomarkers for triple-negative breast cancers (TNBCs). Recently, pembrolizumab, an immune checkpoint inhibitor (ICI) for programmed cell death 1 (PD-1), was approved as a treatment strategy for unresectable or metastatic tumor with high-frequency microsatellite instability (MSI-H) or mismatch repair deficiency, such as malignant melanoma, non-small cell lung cancer, renal cell cancer and urothelial cancer. In addition, results from clinical trials suggested that ICI was a promising treatment for TNBCs with accumulated mutations. However, the frequency of MSI in Japanese TNBCs still remains unclear. We aimed to analyze the presence of MSI-H in TNBCs as a biomarker for ICI therapy.

Methods

In this study, we retrospectively evaluated the MSI of 228 TNBCs using an innovative method, MSI Analysis System Version 1.2 (Promega), consisting of 5 microsatellite markers: BAT-26, NR-21, BAT-25, MONO-27 and NR-24 without a normal tissue control.

Results

Among 228 tumors, 222 (97.4%) were microsatellite stable, 4 (1.7%) low-frequency MSI and 2 (0.9%) MSI-H, respectively. Two MSI-H tumors were potentially aggressive pathologically as indicated by nuclear grade 3 and high Ki-67 (> 30%), and were classified as basal-like and non-BRCA-like, but were not consistent regarding tumor-infiltrating lymphocytes, CD8 and PD-L1 expression.

Conclusions

Although we found that MSI-H was uncommon (0.9%) in TNBCs, potential targets for ICIs exist in TNBCs. Therefore, MSI-H breast cancer patients should be picked up using not only conventional methods but also platforms for comprehensive genomic profiling.

DNA mismatch repair and the transition to hormone independence in breast and prostate cancer

The molecular basis for the progression of breast and prostate cancer from hormone dependent to hormone independent disease remains a critical issue in the management of these two cancers. The DNA mismatch repair system is integral to the maintenance of genomic stability and suppression of tumorigenesis. No firm consensus exists regarding the implications of mismatch repair (MMR) deficiencies in the development of breast or prostate cancer. However, recent studies have reported an association between mismatch repair deficiency and loss of specific hormone receptors, inferring a potential role for mismatch repair deficiency in this transition. An updated review of the experimental data supporting or contradicting the involvement of MMR defects in the development and progression of breast and prostate cancer will be provided with particular emphasis on their implications in the transition to hormone independence.

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 hereditary and sporadic breast cancers

Sporadic cancers and familial breast cancers are characterized by an increase in genetic instability. Little is known about whether mismatch repair defects accompany this genetic instability. We investigated invasive and/or in situ breast cancers from 30 women with deleterious BRCA1/2 mutations and unclassified variant BRCA1/2 alterations. Forty cases of sporadic breast cancers were also investigated, including 7 medullary carcinomas. Malignant and benign lesions were examined from all cases to better understand tumor progression. Automated immunohistochemistry, with antibodies directed against hMLH1 and hMSH2, was used to screen cases for possible mismatch repair defects. When loss of expression was noted, DNA ploidy was performed by cytomorphometry. DNA, after laser microdissection, was extracted from a majority of familial cases and their corresponding controls, and microsatellite instability analysis was performed. None of the familial or sporadic cases had loss of hMSH2 expression. All but one lesion, a DCIS arising in a deleterious BRCA2 mutation carrier, had loss of hMLH1 expression and a tetraploid profile by image cytomorphometry. There was no MSI in any explored lesions (n = 34), as determined by molecular analysis, including the DCIS with loss of hMLH1 expression. We conclude that DNA mismatch repair defects involving hMLH1 and hMSH2 underexpression are extremely rare events in sporadic and familial breast cancer. Mismatch repair gene mutations may be secondary random events in breast cancer progression.

DNA content, chromatin texture and nuclear morphology in benzo[a]pyrene-transformed human breast epithelial cells after microcell-mediated transfer of chromosomes 11 and 17

BACKGROUND

A relation between the changes in DNA content and chromatin supra-organization and the expression of gradual steps of tumorigenesis has been assessed by image analysis in human breast epithelial cells (MCF-10F) treated with benzo[a]pyrene (BP) (cell lines BP1, BP1-E, BP1-Tras, and others).

METHODS

Because abnormal chromosomes 11 and 17 have been associated with neoplastic progression in BP-transformed MCF-10F cells, image analysis of Feulgen-stained tumorigenic BP1-E cells with the microcell-mediated chromosome transfer of normal chromosomes 11 and 17 was carried out.

RESULTS

A tendency of DNA amount distribution and nuclear size restoration to values typical of non-transformed MCF-10F cells was demonstrated, especially after the transfer of chromosome 17. No reversion in chromatin texture was found after the transfer of chromosome 11 or 17.

CONCLUSIONS

Although the presence of a normal chromosome 17 should be considered among the necessary steps for tumorigenic human breast epithelial cells to recover their normality, a more complex genome balance is required for the entire nuclear chromatin of these cells to recover its totally normal supra-organization and expression.

Genetic and epigenetic modification of mismatch repair genes hMSH2 and hMLH1 in sporadic breast cancer with microsatellite instability

Breast cancer is the most common cancer in women, but its pathogenesis is still unclear. Microsatellite instability (MSI) has been identified in breast cancer cells, suggesting an association with mismatch repair defects. To test this hypothesis, we investigated MSI, protein expression of hMSH2 and hMLH1, as well as genetic and epigenetic modifications of these two genes in 32 sporadic breast tumors. MSI was identified in 15 cases. Immunohistochemistry analysis revealed that all MSI cases but one had lower than normal expression of hMSH2 (nine cases), hMLH1 (12 cases), or both (seven cases). In tumors with MSI, both genetic and epigenetic modifications of these mismatch repair genes were also identified. Eight cases harbored mutations or polymorphisms in hMSH2 and hMLH1, and 10 exhibited hypermethylation in the promoter region of hMLH1. These results suggest that both genetic and epigenetic alterations of hMSH2 and especially of hMLH1 contribute to genomic instability and tumorigenesis in sporadic breast cancer.

p53 expression is decreased in primary breast carcinomas with microsatellite instability

p53 and p185 expression in primary breast cancer with microsatellite instability (MSI) is still largely unexplored. To investigate the relationship between these oncoproteins and the pathways of genomic instability, we examined 52 primary invasive breast cancers stratified by the presence and absence of MSI. We determined the status of eight microsatellite loci using radioactive and silver staining methods, and evaluated the immunohistochemical expression of p53 and p185 in a consecutive series of Italian cancer patients characterized by clinical-pathological and biological parameters. Nineteen cases (36.5%) were MSI-positive in at least two loci. p53 was expressed in 15 cases (28.8%) and p185 in eight (15.4%). MSI-positive tumors were inversely correlated with p53 expression (p = 0.0007); in addition, the percent of p53-expressing cells decreased as the number of MSI-positive loci increased. MSI-positive tumors were correlated with a larger tumor size (p = 0.04), lymph-node metastasis (p = 0.001), and advanced clinical stage (p = 0.0006). These data demonstrate the existence of two subsets of primary breast cancers: one characterized by MSI, the other by p53 expression. MSI-positive patients had a more advanced and/or aggressive disease.

Assessment of genomic instability in breast cancer and uveal melanoma by random amplified polymorphic DNA analysis

Some types of cancer have been associated with abnormal DNA fingerprinting. We used random amplified polymorphic DNA (RAPD) to generate fingerprints that detect genomic alterations in human breast cancer. Primers were designed by choosing sequences involved in the development of DNA mutations. Seventeen primers in 44 different combinations were used to screen a total of 6 breast cancer DNA/normal DNA pairs and 6 uveal melanoma DNA/normal DNA pairs. Forty-five percent of these combinations reliably detected quantitative differences in the breast cancer pairs, while only 18% of these combinations detected differences in the uveal melanoma pairs. Fourteen (32%) and 12 (27%) primers generated a smear or did not produce any band patterns in the first and second cases, respectively. Taking into account the ability of RAPD to screen the whole genome, our results suggest that the genomic damage in breast cancer is significantly higher than in uveal melanoma. Our study confirms other reports that the molecular karyotypes produced with random priming, called amplotypes, are very useful for assessing genomic damage in cancer.

Mannose 6-phosphate/insulin-like growth factor 2 receptor, a bona fide tumor suppressor gene or just a promising candidate?

The mannose 6-phosphate/insulin-like growth factor 2 receptor (M6P/IGF2R) is considered a "candidate" tumor suppressor gene. This hypothesis has been provoked by the identification of loss of heterozygosity (LOH) at the M6P/IGF2R locus on chromosome 6q26 in breast and liver cancer, accompanied by point mutations in the remaining allele. Somatic mutations in coding region microsatellites have also been described in replication error positive (RER+) tumors of the gastrointestinal tract, endometrium and brain. These genetic data are compelling, but a tumor suppressor gene candidate has to meet functional as well as genetic criteria. This review weighs the evidence and discusses the observations that are necessary to promote M6P/IGF2R from candidate to bona fide tumor suppressor gene.

Microsatellite alterations in various sarcomas in Japanese patients

To determine the usefulness of microsatellite analysis in the differential diagnosis of various sarcomas, we investigated microsatellite alterations at 12 microsatellite loci by polymerase chain reaction and electrophoresis in 39 Japanese patients with sarcomas. The sarcomas were: osteosarcoma, Ewing's sarcoma, chondrosarcoma, liposarcoma, leiomyosarcoma, epithelioid leiomyosarcoma, rhabdomyosarcoma, synovial sarcoma, and malignant fibrous histiocytoma. We also examined ten leiomyomas to contrast with leiomyosarcoma. No microsatellite instability (MSI) or loss of heterozygosity (LOH) were found in Ewing's sarcoma, chondrosarcoma, epithelioid leiomyosarcoma, malignant fibrous histiocytoma, and leiomyoma. Only three patients, one each with liposarcoma, leiomyosarcoma, and synovial sarcoma, manifested MSI, whereas, osteosarcoma, liposarcoma, leiomyosarcoma, rhabdomyosarcoma, and synovial sarcoma manifested LOH, with an incidence of 43%, 14%, 86%, 20%, and 75%, respectively. Interestingly, three patients showed unusual patterns of LOH, probably due to intratumoral heterogeneity. Kaplan-Meier analysis revealed that LOH on 11p was predictive of poor prognosis in osteosarcoma. The low incidence of MSI indicates that MSI is not necessary for neoplastic transformation in sarcomas. However, the very high incidence of LOH in leiomyosarcoma indicates that microsatellite analysis may serve for the differential diagnosis of leiomyosarcoma versus leiomyoma. Microsatellite analysis may also predict prognosis in osteosarcoma.

Microsatellite instability during the immortalization and transformation of human breast epithelial cells in vitro

The objective of this study was to determine whether microsatellite instability (MSI) and loss of heterozygosity (LOH) are involved in the immortalization of human breast epithelial cells (HBECs) in vitro and in the early stages of their transformation by benzo[a]pyrene (BP) and 7,12-dimethylbenz[a]anthracene (DMBA). We performed a genome-wide analysis of a total of 466 microsatellite DNA polymorphism loci along the X chromosome and the 22 pairs of human autosomes. MSI was found in the immortalized MCF-10F cells at the following loci: D11S1392 (on chromosome 11p13) and D17S849 (at 17p13.3), D17S796 (at 17p13.1), D17S513 (at 17p13.1), TP53 (at 17p13.1), D17S786 (at 17p13.1), and D17S520 (at 17p12) on chromosome 17. The BP-transformed cells exhibited MSI in the same loci and also in locus D11S912 (at 11q25). The more transformed BP1E cells also exhibited MSI on chromosome 13q12-13 at D13S260 and D13S289, markers known to flank the breast cancer susceptibility gene BRCA2. In the DMBA-transformed D3 and D3-1 cells, MSI was observed at the locus D13S260 in addition to the previously reported locus D16S285 (at 16q12.1). No LOH was observed on any of the chromosomes tested in these cells. These observations led us to conclude that the immortalization and transformation of HBECs may involve defects in mechanisms responsible for the cell's genomic stability, such as DNA replication and DNA mismatch repair.

The Clinical Value of Microsatellite Instability and a Loss in Heterozygosity in Sporadic Breast Cancers

We analyzed loss of heterozygosity (LOH) and microsatellite instability (MI) in 108 cases of sporadic breast cancers using 22 microsatellite markers on 12 chromosomes. LOH was frequently seen in 1p(13%), 6p(18%), 8p(11%), 11p(18%), 13q(21%),16q(31%), 17p(44%) and 17q(29%). Individual patients were scored according to the degree of LOH at the above eight chromosomal markers. Patients with no LOH were scored as 1, patients with one to three LOH were scored as 2, and patients with four or more LOH were scored as 3. A high LOH score correlated with a high histological grade (p=0.019) and a poor prognosis (p=0.0035). Eleven(10.2%) of 108 patients with breast cancer showed MI, with 6 cases showing MI at a single locus and 5 at multiple loci. Of the 11 MI-positive patients only one had lymph node involvement(p=0.015), none had histological grade 3 disease, and MI-positive patients tended to have a better prognosis than MI-negative ones. These data suggest that MI may be an early event in mammary tumorigenesis, and that LOH occurs at a later stage. The LOH score may be a useful prognostic marker of operable breast cancer.