Radiotherapy (RT) for Cutaneous Adnexal Carcinoma (CAC): 49 Patients Treated at a Single Institution Over 2 Decades

Abstract

Cutaneous adnexal carcinomas (CACs) are a heterogenous group of rare skin cancers. Management strategies are extrapolated from the treatment of more common skin cancers, and case series describing patients treated with radiotherapy (RT) for CAC are limited to <15 patients. We reviewed our institutional experience to better understand the characteristics and outcomes of patients with CAC treated with RT. Patients diagnosed with CAC and treated RT from 2000-2020 were identified using the following keywords: adnexal, microcystic, apocrine, eccrine, sebaceous, sweat gland, syringoma, mucinous, tubular, porocarcinoma, hidradenocarcinoma, and cylindrocarcinoma. Patient, cancer, and treatment characteristics were assessed by retrospective record review. Time to overall survival (OS), locoregional recurrence (LRR), distant metastasis (DM), and progression free survival (PFS) were evaluated using Kaplan-Meier methods. Forty-nine patients with a median age of 65 years (IQR 53-82) were identified. Most were white (90%) men (59%) harboring tumors on the head and neck (80%). The most common subtypes of CAC were adnexal adenocarcinoma (39%), sebaceous carcinoma (35%) and microcystic adnexal carcinoma (10%). Patients were treated for de novo cancer (n = 35) or after recurrence (n = 14). Among de novo cases, 9 (26%) were treated with definitive RT, 22 (63%) were treated with surgery and adjuvant RT, and 4 (11%) with palliative RT. Per UICC system, de novo stage at time of RT was I in 2 (6%), II in 9 (26%), III in 12 (34%), IVA in 10 (29%), and IVB in 2 (6%). Median OS was 44 months and median follow-up of surviving patients was 41 months (IQR 17-75). De novo patients treated with definitive RT received a median dose of 70 Gy (IQR 60-73 Gy) and experienced 2-year rates of PFS, LRR, and DM of 30%, 55%, and 40%, respectively. All LRR events occurred within the irradiated volume. De novo patients treated with surgery and adjuvant RT received a median dose of 60 Gy (IQR 60-64 Gy) and experienced 2-year rates of PFS, LRR, and DM of 77%, 13%, and 10%, respectively. All LRR events occurred outside the irradiated volume. Among patients treated at recurrence, most (93%) underwent surgery and adjuvant RT. Per UICC system, their stage at time of RT was II in 2 (15.4%), III in 4 (30.8%), and IVA in 7 (53.8%). Recurrent patients treated with surgery and adjuvant RT received a median dose of 60 Gy (IQR 60-66 Gy) and experienced 2-year rates of PFS, LRR, and DM of 30%, 58%, and 29%, respectively. Three of 4 evaluable patients treated with palliative RT exhibited stable disease or tumor response. In the largest single institution analysis to date, RT was primarily used for CAC patients as an adjuvant treatment. LRR was less frequent and less likely to occur within irradiated volume in patients selected for surgery and adjuvant RT than those selected for definitive RT or at time of recurrence.