Is it time to acknowledge intramucosal colorectal carcinoma?

Aim: The term 'intramucosal carcinoma' in the colorectum is controversial when used as a synonym for high-grade dysplasia. However, setting clear definitions for this diagnosis (i.e. unequivocal infiltrative growth in the lamina propria, which might be most easily recognized in cases with overt poor differentiation or formation of signet ring cells or tumour budding) allow us to investigate its relevance.

Methods and results: We reviewed cases from our archive (1990-2024) and selected 14 true intramucosal carcinomas using our strict histological criteria, excluding high-grade dysplasia and invasive carcinomas. These occur primarily in conventional adenomas and are frequently associated with microsatellite instability (50%). Our study shows a low estimated incidence of intramucosal carcinoma (0.01%) in population screening and highlights the low lymph node risk and the good outcome of patients with intramucosal carcinoma.

Conclusion: The rare diagnosis of intramucosal colorectal carcinoma aids in identifying patients at increased colorectal cancer risk, notably those with hereditary syndromes. Standardizing this diagnosis is critical to prevent overdiagnosis and unnecessary treatment.