Epidemiology of Adenosquamous Carcinomas.

Background: Adenosquamous carcinomas (ASCs) are a very rare histology containing cancer cells with both glandular-like (adeno) and squamous cell histologies, comprising typically a fraction of a percent of all solid tumors. The bulk of the literature on ASCs is comprised of case reports and small series, with the general finding that ASCs tend to have worse outcomes than either of their parent histologies. However, there is a lack of pan site-comparative studies in the literature that compare ASC clinicodemographic and survival outcomes with those of conventional adenocarcinomas (ACs) and squamous cell carcinomas (SCCs). Methods: In this study, we summarize these outcomes in eight primary sites, comprising 92.7% of all ASC cases diagnosed from 1975 to 2020 in the Surveillance, Epidemiology, and End Results (SEER) database. Results: Lung ASCs comprise 51.5% of all ASC cases, accounting for 1.1% of all lung cancer cases, followed by uterine/cervical cancers at 29.7% of all ASC cases, translating into 1.8% of all cancers in this site. In descending order, the remaining 20% of ASCs arise in pancreatic, oral cavity, biliary, esophageal, colorectal, and gastric sites, comprising between 0.1% and 0.7% of all cancers in these sites. Apart from pancreatic and oral cavity cancers, ASC tumors tended to favor higher rates of regional or distant disease at presentation with poor tumor differentiation compared to either AC or SCC histologies. After multivariable analysis, adjusting for age, sex, detection stage, grade differentiation, surgery, chemotherapy, and radiotherapy, except for oral cavity cancers, ASCs tended to have worse overall survivals compared to ACs (hazard ratios: 1.1 - 1.6) and SCC (1.0 - 1.3), with colorectal ASCs having the worse overall survival compared to colorectal ACs, with a hazard ratio of 1.4 (95% confidence interval: 1.3 - 1.6). Conclusions: Overall, these results suggest that ASC outcomes are site specific, and in general, tend to have worse outcomes than nonvariant ACs and SCCs even after correction for common clinical and epidemiological factors. These cancers have a poorly understood but unique tumor biology that warrants further characterization.