The prognostic significance of primary tumor site in vulvar cancer: a population-based cohort study.

Objective: To investigate the association of primary tumor site with prognosis in vulvar cancer, stratified by vulvar squamous cell carcinoma (SCC) and non-SCC histological types.

Methods: This population-based retrospective study enrolled patients with vulvar cancer from the Surveillance, Epidemiology, and End Results database between January 2000 and December 2018. The primary outcome was cancer-specific survival (CSS). The prognostic difference between labium majus, labium minus and clitoris groups was investigated using Kaplan-Meier analyses and Cox proportional hazards regression analyses.

Results: A total of 3,465 eligible patients with vulvar cancer were included with a mean age of 54.5 years. Among the 1,076 (31.1%) patients with non-SCC, the multivariate Cox regression analyses showed that labium minus-sited disease (hazard ratio [HR]=1.85; 95% confidence interval [CI]=1.27-2.71; p=0.001) and clitoris-sited disease (HR=2.37; 95% CI=1.47-3.85; p<0.001) were significantly associated with worse CSS, compared with labium majus-sited disease. However, among the 2,389 (68.9%) patients with SCC, no significant association of primary tumor site with CSS was found (p>0.05). Kaplan-Meier analyses also showed that the primary tumor site had a significant prognostic effect in vulvar non-SCC (p<0.001) but not in vulvar SCC (p=0.330).

Conclusion: Among vulvar non-SCC, patients with labium minus-sited disease had a significantly worse prognosis than those with labium majus-sited disease, and a significantly better prognosis than those with clitoris-sited disease. Gynecologic oncologists should consider the prognostic effect of primary tumor site in vulvar non-SCC, and make optimal, personalized treatment and surveillance strategies based on different primary tumor sites.