WNT-Activated Deep Penetrating/Plexiform Melanocytoma (Nevus)

**Semantic type:** Neoplastic Process

**Definition:** A benign melanocytic neoplasm composed of spindle and/or epithelioid melanocytes and melanophages. It is caused by the combined activation of the WNT signaling and MAP-kinase pathways. It occurs in the head and neck region, trunk, extremities, and conjunctiva. It presents with well-circumscribed, darkly pigmented papules. The neoplastic melanocytes form wedge-shaped, fascicular, or plexiform patterns. Lesions with a wedge-shaped pattern extend into the deep reticular dermis. In plexiform spindle cell lesions, the neoplastic melanocytes proliferate in the upper dermis. A junctional component is present in the majority of cases. It rarely progresses to melanoma.