Microcystic adnexal carcinoma misdiagnosed as a "recurrent epidermal cyst": A case report

BACKGROUND Microcystic adnexal carcinoma (MAC) is a rare malignant cutaneous adnexal neoplasm, often presenting as a flesh-colored and slow-growing indurated plaque or cystic nodule in the mid-facial region. Its characteristic indolent presentation usually leads to initial misdiagnosis, resulting in tumor mismanagement and added morbidity due to increased propensity for local invasion. CASE SUMMARY A 63-year-old Chinese male patient with a long-term history of excessive ultraviolet irradiation had received two surgeries for an "epidermal cyst " on his glabella and was presented to our hospital's Dermatology Department for further diagnosis and therapy of the lesion on his glabella. One month ago, his two 7 mm x 7 mm subcutaneous nodules were diagnosed as "recurrent epidermal cysts ", and he underwent local excision surgery. Additionally, he has post medical history of surgery for right clear cell renal carcinoma. According to his biopsy, the patient was diagnosed as MAC in our hospital, and a tumor remnant was found on his wound. He then underwent wide local excision to achieve negative margins and reconstruction of full-thickness flap transplantation for tissue coverage. He remained tumor-free after six months of follow-up. CONCLUSION This case highlights the importance of MAC's possible pathogenic factor of excessive ultraviolet exposure, its differential diagnosis to avoid misdiagnosis and mismanagement to adverse prognosis, the patient's particular medical history of clear cell renal carcinoma, the alert for any tumor recurrence in older patients, and his uncommon multiple nodules mess consisting of two 7 mm x 7 mm subcutaneous nodules, that will enrich the existing knowledge of MAC's clinical features.