Clinicopathological characteristics and outcomes of rare histologic subtypes of gallbladder cancer over two decades: A population-based study

BACKGROUND: There is limited literature about the clinicopathological characteristics and outcomes of rare histologic variants of gallbladder cancer (GBC). METHODS: Using SEER database, surgically managed GBC patients with microscopically confirmed adenocarcinoma, adenosquamous/squamous cell carcinoma and papillary carcinoma were identified from 1988 to 2009. Patients with second primary cancer and distant metastasis at presentation were excluded. The effect of clinicopathological variables on overall survival (OS) and disease specific survival (DSS) were analyzed using univariate and multivariate proportional hazards modeling. All associations were considered statistically significant at an alpha error of 0.01. RESULTS: Out of 4738 cases, 217 adenosquamous/squamous (4.6%), 367 papillary (7.7%), and 4154 adenocarcinomas (87.7%) were identified. Median age was 72 years. Higher tumor grade (grade 2, 3, 4 versus grade 1), higher T stage (T2, T3, T4 versus T1), lymph node positivity (N1 versus N0) and adenosquamous/squamous histology (versus adenocarcinoma) had worse OS and DSS (p < .001). Papillary GBC had better OS and DSS than adenocarcinoma (HR = 0.7; p < .001). Radical surgery (versus simple cholecystectomy) had better OS (HR = 0.83, p = 0.002) in multivariate analysis. OS rates at 3 and 5 years were 0.56 and 0.44 for papillary, 0.3 and 0.22 for adenocarcinoma, and 0.14 and 0.12 for adenosquamous/squamous histology, while DSS rates at 3 and 5 years were 0.67 and 0.61 for papillary, 0.38 and 0.31 for adenocarcinoma, and 0.17 and 0.16 for adenosquamous/squamous subtypes respectively. CONCLUSION: Papillary GBC had better survival outcomes while adenosquamous/squamous GBC had worse survival outcomes compared to gallbladder adenocarcinoma.