Incidence and prognostic factors of hepatoid adenocarcinoma: a population-based analysis

Background: Hepatoid adenocarcinoma (HAC) is a kind of rare extrahepatic adenocarcinoma with hepatocyte differentiation. At present, the incidence and prognostic factors of HAC remain poorly discussed. Methods: We extracted two cohorts from Surveillance, Epidemiology, and End Results (SEER) database by restricting the histology to HAC. One cohort of 258 eligible patients was from SEER 21 Regs Limited-Field Research Data + Hurricane Katrina Impacted Louisiana Cases [2000-2016] to compute incidence, and the other cohort of 121 eligible patients was from SEER 18 Regs Custom Data (with additional treatment fields) [1975-2016] to estimate survival and risk factors. The incidence wad computed by the Joinpoint Regression Program (Version 4.7.0.0). The overall survival (OS) and prognostic factors were analyzed by univariate and multivariate analyses in SPSS 24.0. Results: The overall incidence of HAC between 2000 and 2016 was 0.014 per 100,000 people (95% CI: 0.012 to 0.015). The most common primary site was the lung, followed by the digestive, urinary and reproductive organs, but in the previously published case reports, the stomach was the most common site. The median age at diagnosis was 66 (range, 31-85) years. A total of 28.1% of patients underwent surgery, while 71.9% underwent radiotherapy or/and chemotherapy. The 1-year survival rate of these patients was 35.0%, and the 3-year survival rate was only 16.9%. The median survival time was 5 months (95% CI: 2.97 to 7.03 months). Multivariate analysis showed that age less than 60 years, no distant metastasis, surgery and chemotherapy were independent prognostic factors related to a better outcome. Conclusions: This study suggests that HAC is a rare malignant tumor with poor prognosis, and its most common site is lung. Its incidence is increasing year by year. Age at diagnosis, distant metastases, surgery, and chemotherapy were independent prognostic factors.