Immunohistochemical staining for mismatch repair proteins, and its relevance in the diagnosis of hereditary non-polyposis colorectal cancer

Mismatch Repair System Deficiency Is Associated With Response to Neoadjuvant Chemoradiation in Locally Advanced Rectal Cancer

PURPOSE

Defective mismatch repair system (dMMR) has been shown to have a favorable impact on outcome in patients with colorectal cancer treated with surgery or immunotherapy, with adjuvant chemotherapy being discouraged unless there is nodal involvement. Its impact on radiosensitivity is unknown in patients with colorectal cancer.

METHODS AND MATERIALS

Patients treated for locally advanced rectal cancer between 2000 and 2016 were studied. Reported points included age, sex, clinical and radiologic tumor stages at diagnosis, modalities of neoadjuvant treatment, posttreatment pathologic staging, tumor regression score, and local, distant relapse-free, and overall survival. An inverse probability of treatment weighting propensity score analysis was performed to evaluate the association of mismatch repair proficiency with surgical and clinical outcomes.

RESULTS

Among the 296 patients included, 23 (7.8%) had dMMR. Median follow-up was 43.0 months (interquartile range, 27.9-66.7). Patients with dMMR were significantly younger than the others. After inverse probability of treatment weighting propensity score matching, dMMR patients had higher pathologic downstaging rate (P < .0001), higher tumor regression grade (P = .024), and a longer recurrence-free survival (P < .0001).

CONCLUSIONS

dMRR was associated with significant tumor downstaging after neoadjuvant chemoradiation and with increased recurrence-free survival. dMMR patients may have more radiosensitive tumors.

The nonsense mutation MSH2 c.2152C>T shows a founder effect in Portuguese Lynch syndrome families

The mutational spectrum of the MMR genes is highly heterogeneous, but specific mutations are observed at high frequencies in well-defined populations or ethnic groups, due to founder effects. The MSH2 mutation c.2152C>T, p.(Gln718*), has occasionally been described in Lynch families worldwide, including in Portuguese Lynch syndrome families. During genetic testing for Lynch syndrome at the Portuguese Oncology Institutes of Porto and Lisbon, this mutation was identified in 28 seemingly unrelated families. In order to evaluate if this alteration is a founder mutation, haplotype analysis using microsatellite and SNP markers flanking the MSH2 gene was performed in the 28 probands and 87 family members. Additionally, the geographic origin of these families was evaluated and the age of the mutation estimated. Twelve different haplotypes were phased for 13 out of the 28 families and shared a conserved region of ∼3.6 Mb. Based on the mutation and recombination events observed in the microsatellite haplotypes and assuming a generation time of 25 years, the age estimate for the MSH2 mutation was 273 ± 64 years. The geographic origins of these families were mostly from the Northern region of Portugal. Concluding, these results suggest that the MSH2 c.2152C>T alteration is a founder mutation in Portugal with a relatively recent origin. Furthermore, its high proportion indicates that screening for this mutation as a first step, together with the previously reported Portuguese founder mutations, may be cost-effective in genetic testing of Lynch syndrome suspects of Portuguese ancestry.

Comparison between mononucleotide and dinucleotide marker panels in gastric cancer with loss of hMLH1 or hMSH2 expression

BACKGROUND

DNA mismatch repair deficiency is an important molecular mechanism of genetic instability in gastric cancer, and a high instability at microsatellites is associated with favorable prognosis. We compared mononucleotide and dinucleotide microsatellite instability (MSI) marker panels in 56 paired gastric tumor and normal samples.

METHODS

The mononucleotide marker panel (mono panel) consisted of 8 markers: BAT25, BAT26, BAT40, BAT-RII, NR21, NR22, NR24 and NR27. The dinucleotide marker panel (di panel) contained D2S123, D5S346, D17S250, D17S261, D17S520, D18S34 and D18S58. The NCI panel was used as reference panel.

RESULTS

Among 13 gastric tumors showing no hMLH1 or hMSH2 expression, 8 MSI-H (high) and 5 MSI-L (low) were identified. The analytical sensitivities of the NCI, mono and di panels to detect unstable MSI were 61.5% (8/13), 76.9% (10/13) and 84.6% (11/13), respectively. The size change of allele shift was statistically greater in the mono panel than in the di panel (p = 0.02 by Mann-Whitney U-test). The BAT40 (69.2%, 9/13) and D18S34 (76.9%, 10/13) markers showed high sensitivity for determination of MSI status.

CONCLUSIONS

To improve the detection rate of MSI in gastric cancer with loss of hMLH1 or hMSH2 expression, the kind of MSI marker may need to be considered more, instead of the repetitive type of marker. Thus, an MSI panel designed with a combination of both BAT40 and D18S34 is suggested for providing more accurate and sensitive MSI analysis in gastric cancer.

Distribution of somatic mutations of cancer-related genes according to microsatellite instability status in Korean gastric cancer

In studies of the molecular basis of gastric cancer (GC), microsatellite instability (MSI) is one of the key factors. Somatic mutations found in GC are expected to contribute to MSI-high (H) tumorigenesis. We estimated somatic mutation distribution according to MSI status in 52 matched pair GC samples using the Ion Torrent Ion S5 XL with the AmpliSeq Cancer Hotspot panel.Seventy-five (9.8%) somatic variants consisting of 34 hotspot mutations and 41 other likely pathogenic variants were identified in 34 GC samples. The TP53 mutations was most common (35%, 26/75), followed by EGFR (8%, 6/75), HNF1A (8%, 6/75), PIK3CA (8%, 6/75), and ERBB2 (5%, 4/75). To determine MSI status, 52 matched pair samples were estimated using 15 MSI markers. Thirty-nine MS stable (S), 5 MSI-low (L), and 8 MSI-H were classified. GCs with MSI-H tended to have more variants significantly compared with GCs with MS stable (MSS) and MSI-L (standardized J-T statistic  =  3.161 for number of variants; P  =  .002). The mean number of all variants and hotspot mutations per tumor samples only in GCs with MSI-H were 3.9 (range, 1-6) and 1.1 (range, 0-3), respectively. Whereas, the mean number of all variants and hotspot mutations per tumor samples only in GCs with MSS/MSI-L were 1 (0-5)/0.8 (0-1) and 0.5 (0-3)/0.8 (0-1), respectively.In conclusion, GC with MSI-H harbored more mutations in genes that act as a tumor suppressor or oncogene compared to GC with MSS/MSI-L. This finding suggests that the accumulation of MSIs contributes to the genetic diversity and complexities of GC. In addition, targeted NGS approach allows for detection of common and also rare clinically actionable mutations and profiles of comutations in multiple patients simultaneously. Because GC shows distinctive patterns related to ethnics, further studies pertaining to different racial/ethnic groups or cancer types may reinforce our investigations.

Somatic mosaicism and double somatic hits can lead to MSI colorectal tumors

Some patients happen to have a colorectal cancer with microsatellite instability (MSI), but without any alteration in Mismatch Repair (MMR) system (germline mutation/promoter methylation). We aimed to identify the mechanism of inactivation of MMR genes in those cases. We studied 18 patients with MSI CCR and loss of expression of a MMR protein. DNA was extracted from tumoral and normal colonic material. We studied the 3 main MMR genes in tumors, by sequencing and large rearrangement analysis, and looked for mosaicism. Seven patients lost expression of MLH1, we found 1 mutation in the tumor for 3 patients and 2 mutations in one. Eight patients lost expression of MSH2: we found 1 mutation in 2 patients and 2 mutations in four. In the 5 cases with 2 hits, MSI was due to double somatic hits (n = 3), mosaicism (n = 1) and missed germline mutation (n = 1). Mosaicism was confirmed by HRM analysis, and by finding a germline mutation in one patient's son. We could explain MSI in the tumors of 5 patients (27.8 %). Their follow up and family's surveillance could be adjusted, as the sporadic cases don't require intensive surveillance. We describe the first case of somatic mosaicism after de novo mutation in MSH2.

Aberrant splicing caused by a MLH1 splice donor site mutation found in a young Japanese patient with Lynch syndrome

Lynch syndrome, also known as hereditary non-polyposis colorectal cancer, characterized by predisposition to colorectal cancer and other associated cancers, is an autosomal-dominant disorder mainly caused by germline mutations in DNA mismatch repair (MMR) genes such as MLH1, MSH2, and MSH6. Some mutations that disrupt splice donor or acceptor sites cause aberrant mRNA splicing. These mutations are generally considered as pathogenic ones, however, it is sometimes uneasy to accurately predict their pathogenicity without functional assays, particularly when the mutation is a single nucleotide substitution. In this report, we describe a 25-year-old patient with Lynch syndrome who carries a germline variant in a splice donor site of the MLH1 gene (c.790 + 5 G > T), which was first detected among Asian populations. The immunohistochemical analysis revealed loss of MLH1 protein expression in the tumor. Our splicing assay confirmed that the intronic MLH1 variant actually caused aberrant splicing, supporting its pathogenic effect. Our data accumulate more information on the genotype-phenotype relationships in patients with Lynch syndrome.

Characterization of germline mutations of MLH1 and MSH2 in unrelated south American suspected Lynch syndrome individuals

Lynch syndrome (LS) is an autosomal dominant syndrome that predisposes individuals to development of cancers early in life. These cancers are mainly the following: colorectal, endometrial, ovarian, small intestine, stomach and urinary tract cancers. LS is caused by germline mutations in DNA mismatch repair genes (MMR), mostly MLH1 and MSH2, which are responsible for more than 85% of known germline mutations. To search for germline mutations in MLH1 and MSH2 genes in 123 unrelated South American suspected LS patients (Bethesda or Amsterdam Criteria) DNA was obtained from peripheral blood, and PCR was performed followed by direct sequencing in both directions of all exons and intron-exon junctions regions of the MLH1 and MSH2 genes. MLH1 or MSH2 pathogenic mutations were found in 28.45% (34/123) of the individuals, where 25/57 (43.85%) fulfilled Amsterdam I, II and 9/66 (13.63%) the Bethesda criteria. The mutations found in both genes were as follows: nonsense (35.3%), frameshift (26.47%), splicing (23.52%), and missense (9%). Thirteen alterations (35.14%) were described for the first time. The data reported in this study add new information about MLH1 and MSH2 gene mutations and contribute to better characterize LS in Brazil, Uruguay and Argentina. The high rate of novel mutations demonstrates the importance of defining MLH1 and MSH2 mutations in distinct LS populations.

Screening for Lynch syndrome in colorectal cancer: are we doing enough?

PURPOSE

The purpose of this study was to assess the efficacy of screening for the detection of Lynch syndrome (LS) in an unselected population undergoing surgery for a colorectal cancer.

METHODS

A total of 1,040 patients were prospectively included between 2005 and 2009. LS screening modalities included the Bethesda criteria, immunochemistry (IHC) for MLH1, MSH2, and MSH6, and microsatellite instability (MSI) by using pentaplex markers. Promoter methylation was assessed in tumors with a loss of MLH1 expression. Gene sequencing was offered to patients with abnormal IHC or MSI status without promoter methylation.

RESULTS

A total of 105 patients had an abnormal result: 102 (9.8%) exhibited a loss of protein on IHC and 98 (9.4%) had MSI. A discordant result was observed in 10 patients with eventual proven LS in 6 patients. Loss of MLH1 (n = 64) was due to promoter methylation in 43 patients (67.2%). Overall, of 62 patients with an abnormal result, 38 had genetic sequencing leading to 25 (65.8%) identified with a germ-line mutation. Loss of MSH2 on IHC was associated with a mutation in 78.3% (18 of 23) of cases. Among the 62 patients with abnormal results, 23 (37.1%) did not meet the Bethesda criteria.

CONCLUSIONS

Strict application of the Bethesda criteria does not lead to identification of all patients with LS. IHC and MSI testing are complementary methods and should be used in association to identify potential LS patients.

DNA mismatch repair enzyme immunohistochemistry in colorectal cancer: a comparison of biopsy and resection material

BACKGROUND

Microsatellite instability (MSI) in colorectal cancer (CRC) may be predicted using mismatch repair protein (MMRP) immunohistochemistry (immunostaining), allowing focused genetic investigations and potentially influencing therapeutic interventions. Most laboratories perform immunostaining on surgical resection specimens. Endoscopic biopsy specimens are an alternative tissue source for immunostaining. Given the sensitivity of immunostaining to the degree of tissue fixation, endoscopic biopsy material may produce superior staining, based on faster and more thorough fixation. Moreover, in patients receiving neoadjuvant chemotherapy and/or radiotherapy, endoscopic biopsies may be more useful than surgical resection specimens by allowing assessment of MMR status prior to chemotherapy and/or radiotherapy induced changes in tumours. This study examines whether immunostaining for MMRP expression in CRC is as reliable on endoscopic biopsy material as on surgical resection specimens.

METHODS

Immunostaining for MLH1, PMS2, MSH2 and MHS6 was performed on 112 unselected CRC cases with both endoscopic biopsy and surgical resection material available. A single observer blindly examined intensity and distribution of staining and assessed MMRP expression. Two consultant histopathologists reviewed challenging cases. Endoscopic biopsies and surgical resections were compared using non-parametric statistical analysis.

RESULTS

Immunostaining for all four MMRPs on all 112 cases produced conclusive (i.e., fully interpretable) results in endoscopic biopsies. In surgical resection specimens, 10 stains from nine cases were inconclusive (stains for two MMRPs were inconclusive in one case). In cases where conclusive immunostaining was achieved, there was complete agreement in MMRP status between the endoscopic biopsy and corresponding surgical resection specimens. Overall, MMRP loss was identified in 13% of cases; 11% MLH1, 12% PMS2, 1% MSH2, and 1% MSH6. Immunostaining intensity was significantly higher (p < 0.0005) and the distribution of staining was significantly more uniform (p < 0.0005) on endoscopic biopsy than on surgical resection.

CONCLUSION

Endoscopic biopsy provides equal accuracy and easier interpretation of MMRP expression immunostaining compared to surgical resection specimens.

Lynch syndrome among gynecologic oncology patients meeting Bethesda guidelines for screening

OBJECTIVE

Lynch syndrome (LS) is characterized by a high lifetime incidence of colorectal cancer and gynecologic malignancies such as endometrial and ovarian cancer. Identification of LS families is important as it allows for heightened cancer screening which decreases colorectal cancer mortality. The original 1996 Bethesda guidelines included two gynecologic populations that should be further evaluated for LS: those with endometrial cancer before the age of 45 years and those with two LS-related cancers (i.e. synchronous endometrial and ovarian cancer). Our study aims to estimate the prevalence of LS in these two populations.

METHODS

We utilized a diagnostic algorithm that included immunohistochemistry for mismatch repair protein expression followed by selective evaluation for microsatellite instability and MLH1 gene promoter methylation.

RESULTS

Among 72 eligible patients, 9 (12%) had molecular findings consistent with LS: 6/50 (12%) in the early-onset endometrial cancer group and 3/22 (14%) in the synchronous primary cancer group. In an additional 3 cases, MLH1 silencing was due to promoter methylation: 1/50 (2%) in the early-onset endometrial cancer group and 2/22 (9%) in the synchronous primary cancer group. Of the 9 women with molecular criteria suggesting LS, only three had pedigrees meeting the Amsterdam criteria.

CONCLUSIONS

A diagnostic algorithm can identify patients with LS and those who warrant further genetic testing. Our findings reinforce the recommendation that women diagnosed with endometrial cancer before the age of 45 years and women with synchronous endometrial and ovarian cancer be screened for LS, irrespective of family history.

A study on MSH2 and MLH1 mutations in hereditary nonpolyposis colorectal cancer families from the Basque Country, describing four new germline mutations

Hereditary non-polyposis colorectal cancer (HNPCC) or Lynch syndrome underlies between 2 and 5% of all colorectal cancer. It is inherited as an autosomal dominant condition due to mutations in the mismatch repair genes. Fifty-four non-related index cases, 21 of them fulfilling Amsterdam criteria I or II, were studied. Ten (10/21 = 47.6%) different pathological mutations were found in this group, two of which had not previously been reported--one in MLH1 and the other in MSH2-. In the remaining patients, we also found another family with one of these new mutations, and four additional changes, two of which were also new--a pathological change in MSH2 and a second change of uncertain significance in MLH1-, while the other two changes had already been reported. Of all mutations, eight were found in MSH2 (8/15 = 53.3%) and seven in MLH1 (7/15 = 46.6%), suggesting a slightly greater involvement of MSH2 in HNPCC than MLH1 in our population, in contrast to the results reported by other authors.

Microsatellite instability and mismatch repair protein defects in ovarian epithelial neoplasms in patients 50 years of age and younger

Ovarian malignancies occurring in the setting of hereditary nonpolyposis colorectal carcinoma syndrome typically present in young women, often as the first or "sentinel" cancer, but the frequency of microsatellite instability (MSI) and mismatch repair (MMR) defects in ovarian surface epithelial malignancies in women <or=50 years of age is neither well known nor well tested. Fifty-two ovarian surface epithelial carcinomas, including 4 with synchronous endometrial carcinomas, were identified in patients 50 years of age or younger and evaluated for evidence of MSI and MMR protein deficiency. Each case was tested for MSI by multiplex polymerase chain reaction amplification of the National Cancer Institute reference panel (BAT25, BAT26, D2S123, D5S346, and D17S250) and deficiency of MMR protein expression by immunohistochemistry (MLH1, MSH2, MSH6, and PMS2). MMR protein expression and MSI (in a subset of cases) were also evaluated in 50 unselected ovarian serous tumors of low malignant potential , a tumor common in younger women. Defects in MMR were detected in 5 of 52 (10%) ovarian carcinomas by at least 1 testing method, including 2 of 4 (50%) ovarian cancers presenting with synchronous endometrial cancer. Three of the 5 (60%) ovarian carcinomas were clear cell carcinomas (17% of all pure clear cell carcinomas) and the remaining 2 were high-grade carcinomas with endometrioid and mixed histology. Loss of MSH2 and MSH6 was detected in all of the affected clear cell carcinomas and a synchronous endometrial cancer with endometrioid histology. Loss of 1 or more MMR proteins was initially noted in 10/50 ovarian serous tumors of low malignant potential on tissue microarray, but further testing on full tissue sections showed intact protein expression and microsatellite stability in all informative cases. This study demonstrates a 10% rate of MMR-deficient ovarian cancer in women <or=50 years of age. MMR-deficient ovarian cancer is frequently associated with loss of expression of MSH2 and MSH6 proteins and clear cell histology. The occurrence of MMR inactivation in a significant proportion of ovarian clear cell carcinomas (17% in this study) suggests that this tumor may warrant targeted testing in women <or=50 years of age.

Lumboaortic and iliac lymphadenectomy for lymph node recurrence of colorectal cancer: prognostic value of the MSI phenotype

BACKGROUND

Some patients have isolated lumboaortic and/or iliac lymph node recurrences (ILNR) of colorectal cancer. Current guidelines recommend the use of chemotherapy. The aim of our study was to assess the carcinological results of lymphadenectomy for ILNR and to identify prognostic factors that may be used to select patients for this aggressive surgical approach.

METHODS

Medical notes, pathological findings, and surgical procedure of patients who underwent lymphadenectomy for ILNR of colorectal cancer between 1998 and 2005 were reviewed.

RESULTS

Ten patients (four women) underwent lymphadenectomy for ILNR. Lymphadenectomy was performed after a mean of 37 +/- 16.6 months after colon or rectal resection. Two patients developed a postoperative complication. Mean number of lymph nodes removed was 5.7 +/- 3.3. After a median follow-up of 30.7 months, four patients were alive, including two patients without recurrence at 95 and 96 months after colectomy and two with local and distant recurrences at 114 and 70 months. Among the three patients with microsatellite-unstable (MSI) tumors, two were free of disease at 61 and 81 months, respectively, and one died of recurrent disease 20 months after lymphadenectomy.

CONCLUSION

Lymphadenectomy for ILNR of colorectal cancer is a feasible therapeutic option for selected patients. These preliminary results suggest that resection should be proposed for MSI patients because cure is possible, but to be confirmed, the findings require larger studies.

Detection of microsatellite instability in colorectal cancer using an alternative multiplex assay of quasi-monomorphic mononucleotide markers

Colorectal malignancies demonstrating microsatellite instability (MSI) have a very heterogeneous histological appearance, better prognosis, and altered response to therapy. Consequently, identification of the MSI phenotype is both relevant and interesting as a screening and prognostic tool and as a potential predictive factor of chemotherapeutic response. Several groups have argued for the exclusive use of mononucleotide markers for MSI analysis. In this study, an alternative MSI typing multiplex system of mononucleotide microsatellite repeats was developed. This system obviates the need to compare allelic profiles between tumor and matching normal DNA, rendering MSI analysis amenable to high throughput. The quasi-monomorphic allelic distribution of five alternative mononucleotide markers was evaluated in genomic DNA. Only SEC63 and CAT25 were found to be quasi-monomorphic and were thus combined with BAT25 and BAT26 from the Bethesda panel. Consequently, 177 colorectal cancer samples previously analyzed by the Bethesda panel were tested for MSI using this alternative mononucleotide panel. In an attempt to resolve discordant cases, immunohistochemistry of MLH1, MSH2, and MSH6 was performed. The concordance between both panels reached 99.4% when microsatellite stability and MSI-L were grouped together. These new markers were subsequently multiplexed in a single polymerase chain reaction assay. The resulting mononucleotide fluorescent multiplex MSI assay has high accuracy, reliability, and throughput, thus reducing the time and cost involved in MSI testing.