Case 1 -

Poorly differentiated colon adenocarcinoma in a patient with Hereditary Nonpolyposis Colorectal Carcinoma Wendy Frankel

Case History: A 58 year old man was found at routine colonoscopy to have 2 colon tumors, one in his transverse colon and the other in his rectosigmoid. He was healthy and had no previous medical illnesses. His family history was significant for multiple family members with tumors including colon and endometrial carcinoma, ureter and kidney tumors, skin tumors, and thyroid and brain tumors. The family history met the Amsterdam criteria for the diagnosis of Hereditary Nonpolyposis Colorectal Cancer (HNPCC). Biopsies were performed followed by colectomy. Pathologic findings The colectomy specimen contained 2 tumors measuring up to 9 cm at maximum dimension. Microscopic sections through the rectosigmoid tumor showed an adenocarcinoma with a pushing border that extended into the muscularis propria. There was a surrounding Crohn's-like reaction. The growth pattern of the tumor varied from a diffuse proliferation to sheets to nests of malignant cells with poorly differentiated glands in some areas. Many areas contained intraepithelial lymphocytes. All 28 lymph nodes were negative for metastasis. The rectosigmoid tumor was a T2 carcinoma while the transverse tumor was a T3 carcinoma. Immunohistochemical stains for the mismatch repair proteins were evaluated and MLH1 and PMS2 were present, whereas, MSH2 and MSH6 were absent. The tumor was found to be microsatellite unstable by PCR analysis of tumor DNA and gene sequencing revealed a mutation in MSH2 (942+3a>t) confirming a diagnosis of Lynch syndrome. Family screening revealed the same mutation in 2 of 4 sisters, 2 of 5 brothers, 1 of 2 daughters, 1 of 2 nieces, 1 of 1 nephew, and 1 of 1 grand niece. Clinically, this family can be considered to have both the Muir-Torre variant due to the history of skin tumors in the family (sebaceous adenoma) and the Turcot variant due to the family history of brain tumor (brother with glioblastoma multiforme). Case 1 - Slide 1 Click to view with ImageScope Click to view with a Web-Based Viewer Discussion Hereditary Non-Polyposis Colorectal Carcinoma (HNPCC) is the most common hereditary colorectal carcinoma syndrome and accounts for 2 to 4% of colorectal carcinoma in the United States. Patients with HNPCC are at high risk for developing colorectal and many extracolonic tumors including endometrial carcinoma. The age at onset is early but variable. HNPCC is caused by mutations in the mismatch repair genes. Microsatellite instability (MSI) occurs when tissues acquire numerical nucleotide variability in repetitive DNA sequences due to abnormalities in the mismatch repair proteins. MSI is detected in 50-80% of tumors from patients with HNPCC, and is present in 15-20% of unselected colorectal cancer cases, some of which may be due to Lynch Syndrome. Lynch Syndrome is defined as carcinoma having MSI due to a germline mutation in one of the DNA mismatch repair genes, MLH1, MSH2, MSH6 or PMS2. In sporadic colorectal cancer, MSI is related to epigenetic silencing of the MLH1 gene by hypermethylation of the promoter region. The inability to repair somatic gene mutations raises the possibility that mutations will accumulate within a cell. These accumulated mutations are the underlying basis for cancer development. Because the majority of HNPCC associated colorectal tumors also represent Lynch Syndrome and have an analyzable gene defect, testing for MSI is an important screening/diagnostic tool. MSI testing identifies patients and families who need a detailed study of germline DNA to confirm germline mutation in order to make the diagnosis of Lynch syndrome. The detection of MSI in sporadic colorectal carcinomas has prognostic value in that cancers with a high level of microsatellite instability have an improved overall survival and may have a different response to adjuvant therapy. The National Cancer Institute Workshop on HNPCC Syndrome defined a set of criteria that when met warrant MSI tumor testing. These criteria are known as the Bethesda guidelines. There is evidence that the Bethesda criteria are more sensitive (and less specific) than either the Amsterdam I or II criteria in identifying potential Lynch Syndrome patients and families with pathogenic mutations. Included in the Bethesda criteria are certain histopathologic criteria that help identify MSI colorectal carcinoma, specifically, poorly differentiated or undifferentiated tumors and signet ring cell type colorectal carcinoma. Certain histologic features of microsatellite unstable tumors have been described, including well circumscribed tumors with pushing borders and a prominent host lymphocytic infiltrate. The host reaction can include intraepithelial lymphocytes, peritumoral lymphocytes and/or a Crohn's-like reaction. Some tumors are poorly differentiated with epithelium disposed in small clusters and irregular trabeculae or large aggregates with intraepithelial lymphocytes. This subtype has been described as medullary or undifferentiated, though the majority contains sub-clones in which glandular differentiation is evident. Among the histologic features, mucinous histology and intraepithelial lymphocytosis correlate the most with MSI. Several studies have tried to identify features that can differentiate tumors from patients with Lynch Syndrome from those with sporadic MLH1 promoter methylation. Many authors agree that although Lynch syndrome tumors are more often poorly differentiated, mucin producing, or of the signet ring cell and medullary type, there is no specific histologic type that can differentiate patients with Lynch Syndrome from those with sporadic MLH1 promoter methylation. Columbus area HNPCC study The Columbus Ohio area HNPCC study evaluated all patients with newly diagnosed colorectal carcinoma. In the initial 1066 patients, 19.5% were found to have microsatellite instability (MSI high and low) and 2.2% (23 patients) were found to have HNPCC. Of these 23 patients, 10 were greater than 50 years old and 5 did not meet clinical Amsterdam or Bethesda criteria. The families of 21 HNPCC patients were screened and an additional 52 cases of HNPCC were identified. Therefore, routine screening for HNPCC is useful in unselected colorectal carcinoma patients. Screening using immunohistochemistry was found to be at least as useful as screening by MSI genotyping. Diagnosis In order to detect Lynch syndrome, the family and personal history are vital. Amsterdam Criteria standardize the clinical criteria for diagnosis, while Bethesda Guidelines help identify patients for MSI testing. Both together are less than 50% sensitive in unselected patients. Typical histologic features in microsatellite unstable colorectal carcinomas include intraepithelial lymphocytes, mucinous carcinoma, signet ring cells, medullary carcinomas and tumor heterogeneity. The sensitivity is fairly low (up to 40 %) but the specificity is better (up to 95% with some features). Immunohistochemistry for the mismatch repair proteins can be helpful to direct genetic testing. All proteins are normally present in the colonic epithelial cells. If a protein is absent, the associated protein is not being expressed (mutation or methylation). If any protein is absent, the tumor can be assumed to be microsatellite unstable. MSI analysis can be performed on tumor DNA to detect microsatellite instability. Whether MSI analysis and/or immunohistochemistry are performed initially depends on the center. MSI and immunohistochemistry both have pitfalls. MSI analysis requires a molecular laboratory and normal tissue or blood for comparison while immunohistochemistry does not. Pitfalls in MSI analysis include intratumoral heterogeneity and problems with tumors containing a low percentage of malignant cells including mucinous tumors. Problems with immunhistochemistry include the need for expertise to stain and interpret slides, intratumoral variability in staining, and the interpretation of cytoplasmic staining. Immunohistochemistry has the advantage of being readily available in any pathology laboratory and normal tissue is not needed. Additionally, Immunohistochemistry may be used to direct molecular testing since it predicts the gene likely to harbor a germline mutation. Genetic sequencing and methylation studies can be performed depending on results of the initial studies. MSI analysis beyond HNPCC Microsatellite instability has applicability outside of the detection of HNPCC. It has been demonstrated that microsatellite unstable high tumors have an improved survival as compared with stage matched stable cancers. In addition, recent studies, have suggested an association between low level of microsatellite instability and poor cancer specific survival. Therefore, for prognostic purposes it is useful to determine MSI status on all colorectal carcinomas. While many centers use immunohistochemistry for all four proteins in lieu of MSI (assuming that tumors with any absent mismatch repair protein are MSI positive), this cannot differentiate between tumors that are MSI high and MSI low which may be important if they do indeed have a different prognosis. There remains controversy regarding whether microsatellite unstable carcinomas respond differentially to some chemotherapy regimens as compared with microsatellite stable carcinomas. Conclusion The detection of MSI is important to identify HNPCC and prognosis. Identification is based upon history and laboratory testing. Histopathologic features in MSI colorectal can be recognized and may be useful to identify patients who need further analysis, either with molecular studies or immunohistochemistry. References Alexander J, Watanabe T, Wu T, et al. Histopathological Identification of colon cancer with microsatellite instability. Am J Pathol 2001; 158: 527-35. Boland CR, Thibodeau SN, Hamilton SR, et al. A National Cancer Institute Workshop on Microsatellite Instability for cancer detection and familial predisposition: development of international criteria for the determination of microsatellite instability in colorectal cancer. Cancer Res 1998;58:5248-57. Graham DM, Appelman HD. 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