Incidence and prevalence of neuroendocrine neoplasms in Norway 1993-2021

The incidence of neuroendocrine neoplasms (NENs) has increased over the last decades. The prevalence of NENs has to a lesser extent been previously reported. We wanted to study the trends in incidence and prevalence of NEN in Norway from 1993 to 2021 through the Cancer Registry of Norway. This registry, which covers the whole population, has been found to be 99% complete. The neoplasms were classified as neuroendocrine tumors (NETs) and neuroendocrine carcinomas (NECs). From 1993 to 2021 altogether 10.288 NETs and 13,982 (1.756 outside the lungs) NECs were diagnosed. The incidence of NETs increased from 3.72 to 9.97 per 100,000 per year, corresponding to a 268% increase, p < .001. The largest increase in incidence for NETs was found for pancreas (338%), lung (330%) and small intestine (303%). For NECs there was no change in the incidence, from 9.74 to 9.95 per 100,000 per year, p = .4, but there was an increase in the incidence of NECs originating from the skin (Merkel cell carcinoma) (287%), p < .001, and the GI tract (200%), p = .03. There were no changes in stage distribution at diagnosis for NETs and NECs. The prevalence for NENs increased 666% during the study period, NETs increased from 10.77 to 99.37 per 100.000 (927%), p < .001. For NECs the increase was from 7.4 to 21.56 per 100.000 (291%), p < .001. GI-NECs increased the most from 0.005 to 0.94 (1880%), p = .002. In conclusion, there was a substantial increase in incidence and prevalence of neuroendocrine neoplasms in Norway from 1993 to 2021. This is the first study to report complete prevalence of NENs for a whole nation.