CD10 and CD20 Expression in a Primary Cutaneous Lymphoma of Mature T Cell CD8 Phenotype.

An 85 year‐old woman presented with two pearly papules on her left cheek. The clinical impression was BCC. Biopsy revealed a proliferation of atypical keratinocytes emanating from the epidermis and extending beyond the papillary dermis. A diagnosis of invasive squamous cell carcinoma was rendered. Excison with frozen section margin control was performed. Permanent sections revealed melanoma, at least 2.06 mm in depth, with melanoma in situ extending to all peripheral margins. Upon re‐examination of the initial biopsies, pseudoepitheliomatous epidermal hyperplasia (PEH) with marked squamous atypia was noted. Intimately admixed with the squamous proliferation was a growth of large malignant epithelioid cells. The epitheliod cells lacked pigment production and extended to the shave biopsy margins. This second population of cells was strongly S‐100 positive, diagnostic for amelanotic verrucous melanoma. A revised diagnosis of verrucous malignant melanoma, Clark level III, 0.82 mm in depth was rendered. The patient's course was complicated by multiple positive surgical margins and she ultimately received XRT. This case spotlights the rare occurrence of PEH in conjunction with melanoma. PEH can mask the underlying melanoma and lead to a diagnosis of squamous cell carcinoma. As demonstrated, immunostaining is essential in diagnosis of this difficult tumor.