Tina Bocker Edmonston

Histopathologic Features and Microsatellite Instability of Cancers of the Papilla of Vater and Their Precursor Lesions

The prevalence and development of microsatellite instability (MSI) and underlying mismatch repair (MMR) deficiency in the carcinogenesis of adenocarcinomas of the papilla of Vater and their precursor lesions are not well established. We analyzed 120 ampullary adenomas (31 pure adenomas and 89 carcinoma-associated adenomas) and 170 pure adenocarcinomas for MSI, immunohistochemical expression of MMR proteins and specific histopathologic features. The most common histologic subtype was intestinal (46.5%), followed by pancreatobiliary (23.5%), poorly differentiated adenocarcinomas (12.9%), intestinal-mucinous (8.2%), and invasive papillary carcinomas (5.3%). Eight of 89 adenomas (9%) and 15/144 carcinomas (10%) showed high microsatellite instability (MSI-H), 10/89 adenomas (11%) and 5/144 carcinomas (4%) showed low microsatellite instability (MSI-L), and 71/89 adenomas (80%) and 124/144 carcinomas (86%) were microsatellite stable (MSS). MSI analysis from carcinomas contiguous with an adenomatous component (n=54) exhibited concordant results in 6/8 (75%) MSI-H and 42/46 (91.3%) MSS tumors. Of 14 carcinomas with MSI-H, 7 showed loss of MLH1 and 5/6 (83%) MLH1 promoter methylation, and 2 carcinomas showed simultaneous loss of MSH2 and MSH6. Two carcinomas and 3 adenomas with MSI-H revealed exclusive loss of MSH6. MSI-H cancers were significantly associated with intestinal mucinous subtype (P<0.001), high tumor grade (P=0.003), expansive growth pattern (P=0.044), and marked lymphoid host response (P=0.004). Patients with MSI-H carcinoma had a significantly longer overall survival (P=0.0082) than those with MSI-L or MSS tumors. Our findings indicate that the MSI-phenotype is an early event, which develops at the stage of adenoma and is reliably detectable in the precursor lesion. The MMR deficient molecular pathway of carcinogenesis is associated with a histopathologic phenotype in ampullary cancer, similar to the one that has been well described in colon cancer.

Penetrance and Expressivity of MSH6 Germline Mutations in Seven Kindreds Not Ascertained by Family History

Hereditary nonpolyposis colorectal cancer (HNPCC) is caused by inherited mutations in DNA mismatch-repair genes, most commonly MLH1 or MSH2. The role MSH6 plays in inherited cancer susceptibility is less well defined. The aim of this study was to investigate the penetrance and expressivity of MSH6 mutations in kindreds ascertained through endometrial cancer probands unselected for family history. Detailed pedigrees were constructed for six MSH6 mutation carriers. All reported cancers and precancers were confirmed, and tissues were obtained when available. Tumors were analyzed for microsatellite instability (MSI) and for expression of MSH2, MLH1, and MSH6. MSH6 mutation status was determined for 59 family members. Of these 59 individuals, 19 (32%) had confirmed cancers and precancers. There was an excess of mutation carriers among the 19 affected family members (11 [58%] of 19) compared with those among the 40 unaffecteds (8 [20%] of 40, P=.0065, odds ratio = 5.5, 95% CI = 1.66-18.19). In four of the seven tumors analyzed from mutation carriers other than the probands, MSI and/or MMR protein expression was consistent with the involvement of MSH6. Overall estimated penetrance of the MHS6 mutations was 57.7%. Of the tumors in mutation carriers, 78% were part of the extended HNPCC spectrum. This study demonstrates that MSH6 germline mutations are, indeed, associated with increased cancer risk and that the penetrance of mutations may be higher than appreciated elsewhere. A combination of MSI and immunohistochemistry analyses may be helpful in screening for MSH6 mutation carriers.

Increased Risk for Hereditary Nonpolyposis Colorectal Cancer-Associated Synchronous and Metachronous Malignancies in Patients with Microsatellite Instability-Positive Endometrial Carcinoma Lacking MLH1 Promoter Methylation

Purpose: The aim of this study was to evaluate number and types of synchronous and metachronous malignancies in patients with endometrial carcinoma with and without microsatellite instability (MSI). Experimental Design: From a series of 413 endometrial cancer patients, we identified 94 patients with MSI-positive (MSI+) cancers and grouped them by tumor MLH1 promoter methylation status. These 94 patients were matched by year of surgery to 94 patients with MSI-negative (MSI−) endometrial cancers from the same series. Medical records were reviewed for clinicopathologic information including rates and types of synchronous and metachronous malignancies. Hereditary nonpolyposis colorectal cancer (HNPCC)-associated second and third cancers were analyzed for MSI and MSH2, MSH6, and MLH1 expression for comparison with the corresponding endometrial cancers. Results: The MSI+ and MSI− cohorts were similar with regard to age, race, grade, and histology. Twenty-eight MSI+ endometrial cancers (29.8%) were MLH1 unmethylated. Rates of synchronous and metachronous cancers were also similar in the MSI+ and MSI− groups at 20 and 23%, respectively. However, patients with MSI+ MLH1 unmethylated endometrial cancers had an excess of HNPCC-associated second and third cancers compared with those with MSI+ MLH1 methylated and MSI− endometrial cancers (18% versus 4.5%, P = 0.034, and 2.1%, P = 0.002). Six of seven second tumors from 5 patients with MSI+ MLH1 unmethylated endometrial cancers showed concordant MSI and mismatch repair protein expression status. Conclusions: Our observation that patients with MSI-positive MLH1 unmethylated endometrial carcinoma are at increased risk for HNPCC-associated synchronous and metachronous malignancies suggests inherited cancer susceptibility. These patients and their families may warrant more intense cancer surveillance.

DNA mismatch repair and TP53 defects are early events in uterine carcinosarcoma tumorigenesis

Growing molecular evidence shows that uterine carcinosarcomas are clonal tumors. The carcinoma component has a dominant effect in the aggressive clinical behavior of these tumors. Defective DNA mismatch repair affects up to 30% of endometrial adenocarcinomas. The frequency and importance of defective DNA mismatch repair in the histiogenesis of uterine carcinosarcomas remains controversial. We studied the pattern and frequency of defective DNA mismatch repair and TP53 alterations in the epithelial and mesenchymal components of 28 uterine carcinosarcomas. We found evidence of defective DNA mismatch repair in six cases (21%) with a concordance rate of 83% for carcinoma-sarcoma pairs (κ=0.887, P<0.001). Lack of immunostaining for the MLH1 protein was demonstrated in both components in two of these tumors. TP53 defects were evaluated by 17p deletion analysis and p53 immunostaining. Nineteen carcinoma (68%) and 18 sarcoma (64%) components had evidence of either TP53 allelic loss or p53 overexpression. These defects proved clonal in 76% of cases (κ=0.602, P=0.003). Our results indicate that defective DNA mismatch repair and TP53 defects are common early events in carcinosarcoma tumorigenesis. The high rate of concordance for these molecular defects between the carcinoma and sarcoma components adds to existing molecular evidence that carcinosarcomas are clonal malignancies.

MSI-Testing in Hereditary Non-Polyposis Colorectal Carcinoma (HNPCC)

Genomic instability at simple repeated sequences, termed microsatellite instability (MSI), plays an important role in the analysis of sporadic and hereditary colon cancers. In hereditary non-polyposis colorectal cancer syndrome (HNPCC) more than 90% of cases show MSI, whereas only 10–15% of sporadic colorectal cancers do so. Thus, microsatellite analysis is commonly used as the first diagnostic screening test for HNPCC. In 1997, an international collaborative workshop sponsored by the National Cancer Institute (NCI) proposed a set of guidelines for MSI-testing to improve reliability and reproducibility of the analysis as well to allow comparisons between different studies and different laboratories. In this review we assess the value of current protocols forMSI-testing and discuss some diagnostic pitfalls. Our findings support continued use of the MSI marker panel recommended in 1997. Additionally, MSI-testing should be improved by use of microdissection, which helps to identify additional patients with MSI due to enrichment of tumor cells and therefore increased sensitivity. In our view, immunohistochemical staining for mismatch repair protein expression is not a substitute for MSI-analysis but complements MSI screening and helps direct further testing. In summary, MSI-analysis is a highly sensitive and reliable screening method for HNPCC, that requires a well-equipped laboratory as well as an experienced pathologist. Integration of family history and histo-pathological features is also critical.

Graft-versus-Host Disease-Like Pattern in Mycophenolate Mofetil Related Colon Mucosal Injury: Role of FISH in Establishing the Diagnosis

Mycophenolate mofetil (CellCept®), a commonly used immunosuppressive drug in solid organ transplantation, has recently been shown to cause graft-versus-host disease (GVHD)-like changes in the gastrointestinal tract. On rare occasions, true GVHD has also been documented in the gastrointestinal tract of solid organ transplant patients. Because the treatment for these two entities is different, i.e. removal of the offending agent versus the administration of steroids, proper identification of the cause is imperative. We present a case of mycophenolate mofetil colitis mimicking grade I GVHD of the gut. In our study, we used fluorescence in situ hybridization for the Y chromosome to document the lack of male donor lymphocytes in the female recipient colon biopsy. We suggest that molecular techniques including fluorescence in situ hybridization could be used to discriminate between MMF-related colitis and true GVHD in order to help guide therapy.