Incidence trends and relative survival of colorectal neuroendocrine neoplasms: A population-based study using German cancer registry data.

Neuroendocrine neoplasms (NENs) of the colon and rectum are a heterogeneous group of epithelial neoplasms with neuroendocrine differentiation. They include well-differentiated neuroendocrine tumors (NETs), poorly differentiated neuroendocrine carcinomas (NECs) and mixed neuroendocrine-non-neuroendocrine neoplasms (MiNENs). Our aim was to calculate incidence, incidence trends and relative survival for colonic and rectal NETs, NECs, and MiNENs. We analyzed data covering the entire German population recorded between 2009 and 2021, calculating age-standardized incidence rates, annual percent changes, and the relative 5-year survival probability for the calendar period 2017-2021. Our comprehensive analyses included 12,602 NEN cases, with 59% located in the rectum. NECs, MiNENs and tumors with colonic location showed higher stages. We observed an increase in the incidence of NETs, particularly in patients aged <55 years, and in the incidence of MiNENs, and a constant incidence of NECs. The relative five-year survival was high for rectal NETs (95.9%, 95%-CI 94.6; 97.1) and colonic NETs (81.4%, 95%-CI 78.3; 84.5) and low for colonic NECs (20.5%, 95%-CI 17.6; 23.4) and rectal NECs (19.2%, 95%-CI 15.7; 22.6). The increase in the incidence of NETs might be partly due to colorectal cancer screening, improved diagnostics, and changes in classification of NETs. We attribute the increase in incidence of MiNENs to the recent introduction of this morphological category. Higher stages at diagnosis, a higher proportion of NECs and higher median age at diagnosis may contribute to the less favorable survival probabilities associated with colonic as opposed to rectal location.