Gynecological Cancer

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TU_22_3534 - Adjuvant Radiation Therapy for Vulvar Squamous Cell Carcinoma: Does p16-Positivity Influence Locoregional Control?

Tuesday, October 23
2:45 PM - 4:15 PM
Location: Innovation Hub, Exhibit Hall 3

Adjuvant Radiation Therapy for Vulvar Squamous Cell Carcinoma: Does p16-Positivity Influence Locoregional Control?
M. Dohopolski1, Z. D. Horne2, D. Pradhan3, R. Bhargava3, R. P. Edwards4, J. L. Kelley4, J. T. Comerci4, A. B. Olawaiye4, M. Courtney-Brooks4, M. M. Boisen4, J. L. Berger4, S. E. Taylor4, P. Sukumvanich4, and S. Beriwal5; 1Department of Radiation Oncology, UPMC Hillman Cancer Center, Pittsburgh, PA, 2Department of Radiation Oncology, UPMC Hillman Cancer Center, University of Pittsburgh School of Medicine, Pittsburgh, PA, 3Department of Pathology, University of Pittsburgh Medical Center, Pittsburgh, PA, 4Department of Gynecologic Oncology, UPMC Hillman Cancer Center, Pittsburgh, PA, 5UPMC Hillman Cancer Center, Pittsburgh, PA

Purpose/Objective(s): Vulvar squamous cell carcinoma (VSCC) is a relatively rare malignancy. Human papillomavirus (HPV) has been implicated as a causative factor for a subset of these patients. The purpose of this study is to evaluate if p16-positivity, which is surrogate for HPV infection, predicts for better response rates and survival in women who undergo surgery followed by adjuvant radiation therapy (RT).

Materials/Methods: A retrospective chart review was undertaken of all women treated with adjuvant radiation therapy from 2000-2016 for VSCC at our institution. Available tissue blocks were stained for p16. Each tumor was assigned an H-score according to the College of American Pathologists criteria. P16-positivity was defined as diffuse, strong immunoreactivity within invasive tumor with an H-score of 200+. P16 +/- groups were compared using Chi-squared and t-test. These were correlated with outcomes via Kaplan-Meier with log-rank technique. Time to an event was defined as the time from completion of RT.

Results: Thirty nine women were identified. Median follow up was 25.6 months and 43.3 months for living patients. Ten women (25.6%) had p16+ pathology. The median age at diagnosis was 59.3 years for women with p16+ tumors and 70.2 years for women with p16- tumors (p=0.04). The distribution of stage did not differ by p16-status. The median maximal vulvar dose was 54.4Gy (range: 42.6-63.0Gy). The indication for adjuvant RT was close/positive margins in 19 women (48.7%), positive nodes in 8 (20.5%), and both in 12 (30.8%). The average pathologic tumor size was 2.1cm for p16+ tumors and 3.4cm for p16- tumors (p=0.028). Average margin size was not statistically different. There was a trend towards differences in the average number of pathologically involved lymph nodes, 0.5 vs 1.26 for p16+ vs p16-, p=0.077. Vulvar control rates differed by p16 status at 2 years: 88.9% vs 52.3% for p16+ vs p16-, p=0.041. This translated to a strong trend in differences in two-year locoregional control as well: 77.8% vs 47.4% for p16+ vs p16-, respectively, p=0.064. In women with only one indication for adjuvant RT, this benefit was more pronounced for women with p16+ tumors vs p16-: 2-year locoregional control 100% vs 48.5%, p=0.041. Two-year overall survival was not significantly different between p16+/- cohorts (88.9% vs 64.6%, p=0.405). Survival was impacted by risk factors necessitating adjuvant RT, however. Women with either close/positive margins or positive nodes had a 2-year survival of 80.4% vs 50.0% for women with both risk factors (p=0.044). p16+/- status did not statistically influence survival for women with one risk factor, but survival was numerically different at 2 years (100% vs 73.2%).

Conclusion: p16 positivity appears to be a prognostic factor for locoregional control rates in VSCC treated with vulvectomy and adjuvant radiation therapy for close/positive margins or positive lymph nodes. This benefit was pronounced especially in women with only close/positive margins or positive lymph nodes.

Author Disclosure: M. Dohopolski: None. Z.D. Horne: None. R. Bhargava: None. R.P. Edwards: None. M. Courtney-Brooks: None. P. Sukumvanich: None.

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