Amelanotic Melanoma in the Left Retromandibular Area: A Case Report

Kim, Chul Hann; Kim, Jung Eun; Kim, Sung Keun; Cho, Moon Kyun

Abstract

Amelanotic melanomas comprise only 2% of malignant melanomas and are commonly a difficult clinical diagnosis, due to the lack of melanin pigment typically found in melanomas. Even rarer is the amelanotic malignant melanoma, which may clinically mimic a variety of other less serious cutaneous lesions such as erythema or pruritus, and therefore misdirecting the clinician toward improper treatments and frequently delaying necessary diagnostic biopsy. We report a rare case of amelanotic melanoma occurring in the left retromandibular area with a poor prognosis. A 73-year-old woman presented with a 3-year history of a erythematous lesion in the left retromandibular area. The lesion was surgically removed and biopsy was performed. The biopsy specimen showed atypical, pleomorphic tumor cells with little melanin pigment. On immunohistochemical study, the tumor cells were positive for S-100 protein, HMB-45 and Melan-A. These findings were consistent with amelanotic malignant melanoma. On positron emission tomography/computed tomography (PET/CT), hypermetabolic lesions were found in both the axillary lymph nodes. She was treated with chemotherapy. But four months later, the patient died. Amelanotic melanoma is extremely rare and is more aggressive than pigmented lesions in the similarly stage. The absence of pigmentation in the tumor may result in diagnostic confusion. The clinician should be familiar with the presentation of amelanotic malignant melanoma to facilitate prompt diagnosis. Early diagnosis is crucial since survival is related to tumor thickness and tissue invasion.