Abstract

Cutaneous Melanocanthoma was initially described in 1927 by Bloch and designated as melanoacanthoma by Mishima and Pinkus in 1960. Currently, most authorities consider it a variant of pigmented seborrheic keratosis. Herein, we describe a melanoacanthoma-like lesion with full-thickness keratinocytes atypia. The finding leads to various queries, including whether the differentiation of melanoacanthoma from pigmented seborrheic keratosis is purely academic or provides clinical or prognostic value.

An 82-year-old man presented with a pigmented papule on the face with clinical impression of irritated seborrheic keratosis versus squamous cell carcinoma. Histological features of the biopsy on scanning magnification revealed parakeratosis, acanthosis, papillomatosis, diffuse melanosis, and horn cysts. Significant keratinocyte atypia was noted on higher magnification. Mart-1 preparation showed diffuse intralesional colonization by single melanocytes with extensive dendritic processes. 

The literature review shows sufficient ground to keep the designation, including clinical and dermoscopic features, location, and histologic, immunohistochemical, and ultrastructure findings distinct from pigmented seborrheic keratosis. The occurrence of a malignant variant further crystalizes its place as a separate but related entity. Only one previously reported case is noted in the literature; however, the authors preferred the term “pigmented squamous cell carcinoma with dendritic melanocytes” over malignant melanoacanthoma, perhaps due to the lack of significant histological resemblance to benign melanoacanthoma. Our case bears a marked histologic similarity to its benign counterpart to restore the appellation “malignant melanoacanthoma.” Furthermore, its awareness would avoid misdiagnosis and spur the pathologist to a closer examination, as in scanning magnification, the abundant cytoplasmic melanin may conceal keratinocyte atypia.