Mastocytoma Arising Within a Congenital Nevocellular Nevus

Abstract

<h3>To the Editor.—</h3> We report the appearance of a benign acquired solitary mastocytoma within a congenital nevocellular nevus. This observation is important because the history of a recent change in morphology of a congenital nevus may not always portend malignant degeneration. <h3>Report of a Case.—</h3> A 1-year-old boy was evaluated for the appearance of a new nodule of four weeks' duration within a nevus on the chest, which, according to the patient's mother, had been present since birth. Examination revealed an oval, homogeneous, tan, hairless plaque with a smooth surface and irregular distinct borders on the precordium. The nevus measured 5 cm in greatest diameter. A 0.5-cm flesh-colored nodule was asymmetrically placed within the borders of the nevus (Fig 1, arrows). Biopsy of the nodule revealed nests of nevus cells at the dermoepidermal junction and adjacent to eccrine ducts within the papillary and reticular dermis (Fig 2, arrows). The majority of the dermis within the nodule was infiltrated with a monomorphous sheet of spindle-shaped cells that insinuated between collagen bundles. Leder's chloracetate esterase reaction was strongly positive and clearly