Vulvar Recurrences After Intensity-modulated Radiation Therapy for Squamous Cell Carcinoma of the Anus

Objectives: The objective is to determine localregional control (LRC), distant metastasis free survival, disease-free survival, overall survival (OS), and toxicity for patients with squamous cell carcinoma of the anus treated with definitive chemotherapy and intensity-modulated radiation therapy (IMRT). Materials and Methods: We conducted a retrospective review of patients treated using IMRT for squamous cell carcinoma of the anus at our institution since 2005. Patients with local recurrences were identified and reviewed. The Kaplan-Meier curves were used for LRC and OS. Results: From 2005 to 2014, 52 patients were treated with IMRT-based chemoradiation for squamous cell carcinoma of the anus. Median dose to the primary tumor was 54 Gy. LRC, distant metastasis free survival, OS, and disease-free survival were 92.3%, 88.5%, 86.5%, and 84.6%, respectively, with a median follow-up of 20 months. Two local failures occurred at the anal primary site and 2 in the vulva. Despite subsequent palliative radiotherapy and chemotherapy, neither patient with a vulvar recurrence achieved disease control. Conclusions: In a cohort of patients treated with IMRT-based chemoradiation, 2 vulvar recurrences were identified within the avoided external genitalia despite limited recurrence rates within the cohort overall. This experience suggests that for patients with a locally advanced primary tumor and bulky bilateral inguinal or pelvic disease, the in-transit vulvar dermal lymphatics may be at risk for subclinical involvement and subsequent recurrence. If substantiated by a similar pattern of recurrence at other institutions, the external genitalia may need to be reclassified from an avoidance structure to a clinical treatment volume in patients with locally advanced anal cancer.