Microcystic Adnexal Carcinoma: Prognosis and Epidemiology Analysis of the Surveillance, Epidemiology, and End Results Database from 1973-2014

Abstract

Microcystic adnexal carcinoma (MAC) is a rare infiltrative cutaneous tumor that typically presents on sun-exposed skin. Its risk factors include UV radiation, ionizing radiation and immunosuppression. Due to its rarity, earlier reports have been limited to case reports and small retrospective studies, including an early population study. Thus, we sought to update the population database to investigate the prognosis and epidemiology of MAC. Individual patient data from 687 cases of MAC were obtained from the Surveillance, Epidemiology, and End Results (SEER) Program of the National Cancer Institute from 1973 to 2014. Data on patient characteristics (age, race, gender), tumor characteristics (histological grade, extent of disease, lymph node involvement, location of the primary site), treatment modality (surgery, radiation therapy (RT), and chemotherapy), and survival outcomes were investigated and compared using JMP 13 statistical software (SAS Institute, Inc.). Kaplan-Meier method was used to estimate overall survival (OS) and cancer specific survival (CSS). The log-rank test provided estimates of statistical significance during multivariate analysis. A total of 289 (42%) males and 398 (58%) females were identified, including 605 (88%) White, 22 (3%) Black, 15 (2%) Asian/Pacific Islander, 2 (0.3%) American Indian/Alaska natives, and 43 (6%) unknown race. The median age at diagnosis was 67 years (range 6-103 years). Tumor locations included 522 (76%) head and neck (HN), 45 (7%) upper extremity/shoulder, 28 (4%) lower extremity/hip, 77 (11%) trunk, and 6 (1%) perineum. Respective 5- and 10-year OS rates based on tumor location were 81% and 65% for the HN, 83% and 71% for the upper extremity/shoulder, 82% and 46% for the lower extremity/hip, 99% and 88% for the trunk, and 100% for the perineum (p=0.02). 540 (79%) patients received surgery alone, 47 (7%) received both surgery and post-operative RT (PORT), 1 received trimodality (surgery, PORT, and chemotherapy), 2 received RT alone, and 1 received chemotherapy alone. The 5- and 10-year OS rates of surgery vs. surgery and PORT were 84% and 68% vs. 79% and 65%, respectively (p=0.01). The 5-, 10-, and 15-year OS and CSS rates of all patients were 83%, 67% and 50%, and 97%, 95%, and 95%, respectively. To the best of our knowledge, this is the largest database analysis of MAC. This study demonstrated that MAC is mainly a locally invasive disease with rare metastasis to lymph nodes or distantly. MAC has a long course of disease with favorable OS and CSS. The primary management remains surgical resection, though this study suggests PORT may improve outcomes in high risk patients.