Histopathological Changes from Skin-Directed Therapies in Patients Treated for Mycosis Fungoides

Summary: Skin-directed therapies (SDTs) have been shown to be highly effective for managing early-stage mycosis fungoides (MF), involving single or combination usage of the following agents: topical corticosteroids, topical mechlorethamine, topical imiquimod, topical retinoids, total skin electron beam, and phototherapy. When using SDTs, it is important to note their associated histopathological changes on follow-up biopsies to assess for treatment response. We present a case report and literature review of SDT-associated histopathological changes. A 68-year-old male with stage IB MF treated with NBUVB phototherapy, mechlorethamine gel, and oral bexarotene presented for evaluation of suspected MF recurrence on his right lower back. A punch biopsy revealed orthokeratosis with mild patchy spongiosis and scattered apoptotic spinous layer keratinocytes. The latter finding is consistent with changes due to treatment with mechlorethamine gel. In the literature, other reports of methchlorethamine-related histopathologic changes include epidermal hyperplasia, keratinocyte atypia, increased melanophages, enlarged junctional melanocytes, blood vessel dilatation, atypical fibroblasts, and lymphomatoid papulosis. This case reports the rarely discussed histopathologic changes associated with use of topical mechlorethamine. We emphasize the importance of reviewing expected histopathological findings from various MF treatments, which may impact evaluation of pre- and post-treatment biopsies in MF follow-up.