Human papillomavirus infection mediates response and outcome of vulvar squamous cell carcinomas treated with radiation therapy.

ABSTRACT

PURPOSE: Human papillomavirus (HPV) is implicated as a causative factor in vulvar squamous cell carcinoma (VSCC). This study evaluates if p16-positivity, a surrogate for HPV, predicts for better response rates to chemoradiation therapy and survival. MATERIALS AND METHODS: We conducted a retrospective chart review of women treated with neoadjuvant or definitive chemoradiation (CRT) therapy from 2000 to 2016 for VSCC. p16 stain-positivity was defined as diffuse strong "block" immunoreactivity within invasive tumor. RESULTS: Seventy-three women with median follow-up of 13.4 months were analyzed. Thirty-three (45.2%) had p16+ tumors. Median age was 73 years (range 37-89); with p16+ tumors, the median age was 60 years vs 73 years for women with p16- tumors (p < 0.001). The distribution of tumor size and stage by p16-status were similar. The complete clinical response (cCR) rate for p16+ tumors was 63.6% vs 35.0% for p16- tumors (p = 0.014). The pathologic complete response (pCR) rate for women treated neoadjuvantly was 53.8% vs 31.4% for p16+ vs p16-, respectively (p = 0.067). The combined complete response (cCR orpCR [CCR]) rate was 63.6% for p16+ and 30.0% for p16- (p = 0.004). Two-year vulvar control (VC) for women with p16+ tumors was 75.5% vs. 49.5% for p16- (p = 0.008). In women with p16+ tumors who achieved CCR, 2-year VC was 92.3% vs 52.1% for CIR (p = 0.009). For p16- tumors, 2-year VC was 67.3% vs 41.1% for CCR and CIR (p = 0.072). No woman with a p16+ tumor developed distant metastases vs. 7 with p16- tumor (p = 0.013). OS was not statistically different between p16+ cohorts, but was improved for p16- patients with CR vs CIR, 72.9% vs 18.8% (p = 0.026). CONCLUSIONS: p16-positive tumors appear to have better clinical and pathologic response rates and clinical outcomes.