Scaly Erythematous Lesion in a Patient With Extensive Solar Damage

REPORT OF A CASE A 71-year-old white man with a history of multiple actinic keratoses, basal cell carcinomas, and squamous cell carcinomas of the head, trunk, and extremities presented with a slightly raised, erythematous, poorly circumscribed, scaly plaque (4×2 cm in diameter) on the right side of his chest ( Figure 1 ), of uncertain duration. A biopsy specimen was obtained from the center of the lesion. Histologic findings are depicted in hematoxylin-eosin-stained sections ( Figure 2 ). What is your diagnosis? DIAGNOSIS: Malignant melanoma in situ, amelanotic type. HISTOPATHOLOGIC FINDINGS Routine histologic examination showed a markedly atrophic epidermis with hyperkeratosis and focal parakeratosis. There was a diffuse, broad proliferation of melanocytes arranged as single cells or in irregular nests along the dermoepidermal junction and at higher levels of the epidermis. The cells had abundant, clear cytoplasm without evident melanin pigment and hyperchromatic nuclei with prominent eosinophilic nucleoli. The dermis contained abundant