Non‐melanocytic mimics of melanocytic neoplasms

Abstract

On histopathologic examination, many non-neoplastic conditions mimic benign or malignant neoplasms. Alternatively, some benign and malignant neoplasms can also mimic non-neoplastic lesions. This is true of all organ systemsskin is no exception. Examples of these mimickers can be found in skin lesions of almost all tissue types, including those that are melanocytic, lymphoid, epithelial, neural, vascular, neuroendocrine, and fibrohistiocytic. Melanocytic neoplasms are particularly important as it's challenging to differentiate them as being benign or malignant, and it's difficult to tell them apart from non-melanocytic neoplasms. This review illustrates examples of non-melanocytic lesions that disguise themselves as melanocytic.

Matrical carcinoma with melanocytic hyperplasia mimicking nodular melanoma in an elderly Mexican male

“…There are a number of pigmented epithelial, neural/neuro‐ectodermal, mesenchymal, fibrohistiocytic and lymphoid neoplasms, both malignant and non‐malignant, that may mimic melanoma from a clinical and/or histological standpoint. These include, but are not limited to, pigmented: seborrheic keratoses, melanoacanthomas, basal cell carcinoma, MCC, trichoblastoma, pilomatrixoma, apocrine hidrocystoma, nodular hidradenoma, eccrine poroma, actinic keratosis, bowenoid papulosis, squamous cell carcinoma, dermatofibroma, Bednar tumor, epithelioid angiosarcoma, atypical fibroxanthoma and Paget/extramammary Paget disease . As in the present case, if the source of the pigmentation is melanocytes, careful examination of the melanocyte cytology will show their presence as mere hyperplastic bystanders compared to the atypia characteristic of a nearby malignant proliferation.…”

Metastatic melanoma with balloon/histiocytoid cytomorphology after treatment with immunotherapy: A histologic mimic and diagnostic pitfall

“…Furthermore, melanocytes may occasionally acquire nonmelanocytic differentiation, including schwannian, fibroblastic/myofibroblastic, smooth muscle, rhabdomyoblastic, osteocartilaginous, ganglionic/ganglioneuroblastic, neuroendocrine and epithelial features . Different combinations of the above features may result in ambiguous patterns that allow melanoma tom simulate virtually any epithelial, vascular, mesenchymal, neural, hematologic or germ‐line neoplasm, especially in the absence of an epidermal component and/or pigmentation …”

The Spectrum of Spitz Melanocytic Lesions: From Morphologic Diagnosis to Molecular Classification

“…Other lesions displaying epithelioid or spindle cell morphology are also on the differential, one example being epithelioid fibrous histocytoma which also features abundant eosinophilic cytoplasm and scattered mitotic figures ( 51 ). Some non-melanocytic lesions, such as extramammary Paget’s, melanoacanthoma, or Bowen’s disease, may demonstrate pseudo-melanocytic nests, pagetoid spread, and increased melanocytes leading to potential misdiagnosis of a Spitz lesion ( 52 ).…”