Adnexal carcinoma (AC) is a rare subset of cutaneous malignancies derived from skin adnexa. There are limited data on the role of adjuvant radiation therapy (RT). This study investigates outcomes associated with adjuvant RT at our high-volume referral center. Using an institutional pathology database we identified 45 patients with locoregionally-confined AC treated between 2001-2020 with curative intent surgery and RT at initial diagnosis or at the time of locoregionally-confined recurrence. Clinicopathologic variables were described and time to relapse events were assessed by the Kaplan-Meier method. Median age was 64 yrs (IQR 57-71). Primary tumors were in the head and neck (H&N, n = 36, 80%), trunk/extremities (n = 8, 18%) or unknown (n = 1). The most common histologic subtypes were: sebaceous-14 (31%), microcystic adnexal carcinoma-9 (20%), eccrine-6 (13%), and trichilemmal-5 (11%). Twenty-two (50% of known primaries) had PNI. All patients had primary tumor excision. Six had clinically evident lymphadenopathy (13%), all of whom had lymph node dissection (LND). Five patients without evidence of nodal disease (13%) had sentinel lymph node biopsy (SLNB) with one having SLN+ disease. Thirty patients (67%) received adjuvant locoregional RT at initial diagnosis with the following targets: 21 (30%) primary only, 4 (13%) nodal only, and 5 (17%) both. Of those receiving nodal RT, 7 (78%) had LN+ LND with 2 of those receiving concurrent platinum-based chemoradiation. Sixteen were treated at recurrence with the following targets: 4 (25%) primary only (1 having had prior adjuvant nodal RT), 4 (25%) nodal only, and 8 (50%) both. Across the full cohort, median RT dose was 60 Gy in 30 fractions. Median follow-up from initial surgical resection was 60 months (IQR 30-160). 5-year LC, NC, DFS and DSS were 71%, 86%, 66%, and 91% respectively. The only evaluated factor associated with better outcome was adjuvant primary site RT (5-yr LC 83% vs. 56%, p = 0.01 and 5-yr DFS 83% vs. 46%, p = 0.0003). All 15 patients with local recurrence (LR) had salvage surgery with median subsequent follow-up of 75 months (IQR 2-94). Overall, 5 patients receiving adjuvant primary site RT at any time (initial or salvage) developed subsequent local recurrence (13%). Of the 8 patients who developed nodal recurrence (NR) during follow-up, 1 received adjuvant nodal RT at initial diagnosis. Six of 7 who did not receive prior RT then received adjuvant nodal RT after LND and only 1 developed subsequent NR. AC is a rare skin cancer with a primarily locoregional recurrence pattern. In our experience, adjuvant RT was associated with improved LC which, depending on the tumor location, may help prevent morbid or cosmetically-impactful salvage surgery. Patients with AC would benefit from radiation oncology referral to discuss adjuvant treatment.
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