Histologic comparison of hereditary nonpolyposis colorectal cancer associated with MSH2 and MLH1 and colorectal cancer from the general population

PURPOSE: Hereditary nonpolyposis colorectal cancer is reported to have special histologic features. This study compares the histologic features of hereditary nonpolyposis colorectal cancer to colorectal cancers from the general population when hereditary nonpolyposis colorectal cancer cases are restricted to families with known MSH2 and MLH1 mutations. METHODS: Thirty- seven cancers from kindreds carrying MSH2 mutations, 27 cancers from kindreds carrying MLH1 mutations, and 37 colorectal cancers from the general population were reviewed by a pathologist blinded to hereditary nonpolyposis colorectal cancer gene status. Tumor grade, growth pattern, Crohn's-like lymphoid reaction, mucin production, extent of disease in the bowel wall, and lymph node status were evaluated. RESULTS: Poor differentiation and Crohn's- like reaction were a feature of 44 and 49 percent of hereditary nonpolyposis colorectal cancer compared with 14 percent (P = 0.002) and 27 percent (P = 0.049) of colorectal cancers from the general population, respectively. There was no difference in growth pattern, mucin production, lymph node involvement, or local extent of disease between hereditary nonpolyposis colorectal cancer and colorectal cancers from the general population. Poor differentiation and lymph node metastases were found in 57 and 49 percent of MSH2 compared with 26 percent (P = 0.002) and 10 percent (P = 0.03) of MLH1- associated cancers, respectively. There was no difference in growth pattern, mucin production, Crohn's-like lymphoid reaction, or local extent of disease between subgroups of hereditary nonpolyposis colorectal cancer. CONCLUSIONS: Poor differentiation and Crohn's-like reaction are more common in hereditary nonpolyposis colorectal cancer than colorectal cancers from general population. Poor differentiation and lymph node metastases are more commonly seen in MSH2-associated cancers than MLH1. Evaluation of the natural history, pathogenesis, and prognosis of colorectal cancer in hereditary nonpolyposis colorectal cancer should include consideration of which mismatch repair genes are mutated and what the specific mutations are.