Extrapulmonary neuroendocrine carcinomas (NECs) are poorly studied and are managed similar to lung NECs, which may not account for differences between the 2 groups of tumors as well as the heterogeneity within extrapulmonary NEC.

Data from the Surveillance, Epidemiology, and End Results program between 1973 and 2012 were used to estimate the relative percentages of lung NECs and subgroups of extrapulmonary NECs, epidemiological patterns at these sites, and the median and 5-year overall survival rates.

Of 162,983 NEC cases, 14,732 were extrapulmonary; of these, 5509 were gastrointestinal (37.44%), 4151 were of unknown primary (28.2%), and 5072 were of other sites (34.4%). Lung NEC had the highest percentage of small cell morphology (95.2%) and gastrointestinal NEC had the least (38.7%), with the rest being other morphologies. Significant differences were noted with regard to median age (range, 48-74 years), percentage of cases of distant stage disease (24%-77%), and incidence according to sex and race. The median survival of patients with lung NEC was 7.6 months, that for patients with gastrointestinal NEC was 7.5 months (range, 25.1 months for NEC at the small intestine to 5.7 months for NEC at the pancreas), and that for patients with unknown NEC was 2.5 months. The 5-year survival rate for patients with local stage disease ranged from 58% to 60% for NECs of the female genital tract and small intestine to 25% for esophageal NECs. The primary tumor site remained statistically significant for survival even after adjusting for known prognostic variables (P<.0001).

To the authors' knowledge, the current study is the largest study of NECs performed to date and also the first with comprehensive epidemiological data. Significant differences in incidence patterns and large variations in survival depending on anatomical site and morphological subtype were noted. A curative approach is possible for patients with nonmetastatic NECs. Cancer 2018;124:807-15. © 2017 American Cancer Society.