Microcystic Adnexal Carcinoma on the Forehead Misdiagnosed as Cylindroma: A Case Report

Microcystic adnexal carcinoma (MAC) is a rare infiltrative cutaneous malignant tumor that presents as scar-like papules or plaques on sun-exposed skin. MAC can be misdiagnosed as a benign adnexal tumor, owing to its histopathologic similarity and slow growth rate. Nonetheless, MAC can show aggressive local invasion. Therefore, MAC should be treated with surgical excision or radiation therapy. Herein, we report the case of a 51-year-old woman with a flesh-colored plaque on her forehead. The patient was diagnosed with a benign adnexal tumor on the first punch biopsy. Notably, after a second incisional biopsy, the patient was finally diagnosed with MAC. This case demonstrates the difficulty of diagnosing MAC, suggesting that MAC should be considered for the differential diagnosis of slow-growing tumors in the head and neck and that multiple biopsies are needed when histological findings are ambiguous.