Distinct clinicohistologic features of inflammatory bowel disease-associated colorectal adenocarcinoma: in comparison with sporadic microsatellite-stable and Lynch syndrome-related colorectal adenocarcinoma.

Long-standing inflammatory bowel disease (IBD), either ulcerative colitis or Crohn disease, is associated with a high risk of developing colorectal adenocarcinoma (CAC). However, histomorphology of IBD-associated CAC has not been thoroughly examined, and it is unclear whether and how these patients should be screened for Lynch syndrome (LS). We evaluated the demographic and morphologic features of 108 IBD-associated CACs, including ulcerative colitis-associated (n = 95) and Crohn disease-associated CACs (n = 13), against 93 control cases of sporadic microsatellite-stable (MSS) CAC, 20 cases of sporadic microsatellite instability high (MSI-H) CAC, and 23 CAC cases of LS. The mean age of patients with IBD-associated CAC was 50 years, which was lower compared with the mean age of 63.7 years of the sporadic MSS controls and 76.5 years of the sporadic MSI-H group but not statistically different from that of the LS patients. Synchronous CACs were noted in 20.4% of the IBD patients and 13% of LS patients but in only 2.1% of the sporadic MSS controls and in none of the MSI-H patients. Right-sided CACs were significantly less frequent in the IBD group than in sporadic MSS controls, MSI-H group, and LS patients (P < 0.05 for all). In contrast to sporadic MSS CAC, IBD-associated CACs are characterized by lack of tumor necrosis, Crohn-like reaction, tumor histologic heterogeneity, the presence of mucin, and signet ring cell differentiation and tumor well differentiation. The histomorphologic similarity among IBD-associated and MSI-H tumors, either sporadic MSI-H or LS-related, is independent of MSI status. The young age of patients with IBD-associated CAC and the morphological similarities among IBD-associated, sporadic MSI-H, and LS-related CAC suggest that an age-based and morphology-based strategy before the screening test for LS may be less effective in IBD patients than in the non-IBD population.