Adenosquamous Carcinoma of the Stomach: A Population-based Study from the SEER Database

Purpose: Gastric adenosquamous carcinoma (ASC) is a rare pathological type with poorly understood clinicopathological features. The purpose of this study is to identify the characteristics of gastric ASC patients. Methods: Using the Surveillance, Epidemiology, and End Results (SEER) database (2000 to 2014), patients with ASC (N=93) or adenocarcinoma (AC) (N=41794) of the stomach were included. The epidemiology, tumor features, treatment, and outcomes between these two groups were compared. Results: The incidences of ASC from 1983 to 2014 [annual percentage change (APC) = -3.5%, 95% confidence interval (CI) -4.9 to -2.1] and AC from 1973-2014 [APC = -1.8%, 95%CI -2.0 to -1.6] decreased over time. Compared to AC cases, patients with ASC were more likely to present poor differentiation (74.2% vs 52.4%) and later summary stage (distant: 46.2% vs 33.6%) or later T stage (T4: 15.1%% vs 9.0%). Besides, the proportion of patients with distant metastasis (33.3% vs 23.9%), and chemotherapy (44.1% vs 34.0%) in ASC group was higher. The Kaplan-Meier analyses showed ASC cases had worse overall survival (OS) (p=0.017) than that of AC after propensity score matching (PSM), but not the cancer-specific survival (CSS) (p=0.849). The further subgroup analyses suggested no statistical significance between gastric ASC patients and AC patients for CSS. The multivariate cox proportional hazard analyses indicated that patients with distant summary stage (HR=2.11, p=0.014), no surgery (HR=2.22, p=0.016), and no/unknown chemotherapy (HR=3.33, p<0.001) were associated with poor OS for ASC population alone. However, for CSS, only ASC cases with no/unknown chemotherapy (HR=2.22, p=0.018) indicated worse outcomes. Conclusions: Gastric ASC presented more aggressive clinicopathologic characteristics and poorer OS compared with AC. The localized/regional summary stages and undergoing surgery suggested favorable OS for gastric ASC patients. ASC cases receiving chemotherary showed both better OS and CSS.