Incidence, clinicopathological characteristics and survival outcome of rare histological variants of gastric carcinoma: a SEER population-based study

Abstract

Objectives Many histological variants exist apart from adenocarcinoma of the stomach and were previously reported to affect about 5% of gastric cancers. This study aimed to investigate the incidence, clinicopathological characteristics and prognosis of rare histological variants of gastric carcinoma (RGCs).

Methods The Surveillance, Epidemiology, and End Results Program(SEER) databases between 1973 - 2015 were analysed. The age-adjusted incidence rates were calculated per 100,000 population. A total of 830 RGCs were identified for clinicopathological characteristics analysis. Of these, 71 RGCs were selected for prognostic analysis. The effect of clinicopathological variables on overall survival (OS) and disease-specific survival (DSS) were calculated using univariate and multivariate proportional hazards models. A P value of <0.05 was considered statistically significant.

Results RGCs in United States comprised less than 0.1 per 100,000 person-years (age-adjusted) and accounted for 0.46% (830 / 180930 cases) of all gastric tumors. Undifferentiated carcinoma (N=408, 49.2%) appeared as the most frequent histology. Among 71 selected cases for prognostic analysis, age and histological type were independent prognostic factors for 5-yr OS and 5-yr DSS (age, P<0.01; histological type, P<0.01 for 5-yr OS; age, P<0.01; histological type, P=0.01 for 5-yr DSS). T stage was not a prognostic factor for both 5-yr OS and 5-yr DSS in univariate analysis(P=0.82 and P=0.71). Although N stage was a prognostic factor for 5-yr DSS(P=0.02) and showed a trend for 5-yr OS(P=0.09) in univariate analysis, it was not an independent prognostic factor on multivariate analysis.

Conclusions RGCs accounted for 0.46% of all gastric tumors in United States. Medullary carcinoma was the best prognostic histological type. T and N classification failed to demonstrate stratifications on prognosis.