Abstract
Pigmented epithelioid melanocytoma (PEM) is a tumor encompassing epithelioid blue nevus of Carney complex (EBN of CNC) and was previously termed animal-type melanoma. Histologically PEMs are heavily pigmented spindled and epithelioid dermal melanocytic tumors with infiltrative borders, however, their origin remains unclear. Stem cells for the epidermis and hair follicle are located in the bulge area of the hair follicle with the potential to differentiate into multiple lineages. Multiple cutaneous carcinomas, including follicular cutaneous squamous cell carcinoma (FSCC), are thought to arise from stem cells in the follicular bulge. We present two cases of PEM/ATM in a 63 year-old male on the scalp with follicular origin and a 72 year-old female on the upper back arising in an intradermal nevus. Biopsy of both cases revealed a proliferation of heavily pigmented dermal nests of melanocytes with atypia. The Case 1 tumor was in continuation with the outer root sheath of the hair follicle in the bulge region. Case 2 arose in an intradermal melanocytic nevus. Rare mitotic figures, including atypical mitotic figures, were identified in both cases. We present two cases of PEM, with histologic evidence suggesting two origins: one from the follicular bulb and one from an intradermal nevus.
Highlights
Pigmented epithelioid melanocytoma (PEM), known as pigment synthesizing melanoma [1,2,3,4], is an entity encompassing epithelioid blue nevus and previously termed animal-type melanoma (ATM) [5,6]
PEM has been reported to frequently be found in sentinel lymph nodes (SLNs), a short-term follow-up suggests a better prognosis than conventional melanoma [6]
We present two cases of PEM/ATM with histology suggesting a possible origin in the follicular bulge and an intradermal nevus
Summary
Pigmented epithelioid melanocytoma (PEM), known as pigment synthesizing melanoma [1,2,3,4], is an entity encompassing epithelioid blue nevus (of Carney complex) and previously termed animal-type melanoma (ATM) [5,6]. PEMs show a striking histological similarity to ATM [7,8,9] and epithelioid blue nevi [10,11,12]. Studies comparing PEM and epithelioid blue nevi have been unable to find histologic criteria separating metastasizing from nonmetastasizing PEMs [6]. The tumor may either abut the epidermis or be separated by a Grenz zone [6]. The origin of these tumors remains unclear [6]. We present two cases of PEM/ATM with histology suggesting a possible origin in the follicular bulge and an intradermal nevus. The hypothesis of follicular origin is discussed in the context of melanoma origin in rodents
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