Non‐conventional dysplasia is frequently associated with low‐grade tubuloglandular and mucinous adenocarcinomas in inflammatory bowel disease

Aims There is limited information regarding the clinicopathological features of low‐grade tubuloglandular (LGTGA) and mucinous (MAC) adenocarcinomas occurring in inflammatory bowel disease (IBD), especially with regard to their precursor lesions. Methods and results Forty‐six IBD colectomy specimens with LGTGA ( n = 17) or MAC ( n = 29) with adjacent precursor lesions were analysed. As controls, 12 IBD colectomy specimens with well‐ to moderately differentiated adenocarcinoma that lacked any mucinous, signet ring cell, low‐grade tubuloglandular or serrated features were also analysed. Compared with MACs and controls, LGTGAs more often had a flat/invisible macroscopic appearance (LGTGAs = 88%, MACs = 34%, controls = 25%, P < 0.001). MACs were more likely to have high‐grade differentiation (MACs = 31%, LGTGAs = 0%, controls = 0%, P = 0.002) and a higher pathological stage (pT3 and pT4 MACs = 76%, LGTGAs = 35%, controls = 33%, P = 0.007) than LGTGAs and controls. LGTGAs (70%) and MACs (53%) were more frequently associated with non‐conventional dysplasia than controls (0%) ( P < 0.001). Crypt cell (40%) and hypermucinous (34%) dysplasias were the most common non‐conventional subtypes associated with LGTGAs and MACs, respectively. Synchronous dysplasia often demonstrated non‐conventional features in the LGTGA (33%) and MAC (47%) groups (versus 0% for the control group, P = 0.074). Synchronous cancer frequently showed similar histological features as the main tumour (LGTGA group = 60%, MAC group = 38%, control group = 100%). Conclusions Crypt cell and hypermucinous dysplasias are the most common precursor lesions associated with LGTGAs and MACs, respectively, and may serve as a marker of increased risk for these cancer subtypes.