Abstract

In patients with folliculotropic mycosis fungoides (FMF), there is a recurrence rate of 15.8%. In addition, FMF is an independent predictor of poor survival and increased risk of disease progression. When a patient presents with a new T-cell lymphoproliferative disorder, determining recurrence versus a new primary can be difficult. We report a patient with a history of FMF presenting with a distinct peripheral T cell lymphoma, not otherwise specified. An 82-year-old male with a history of squamous cell carcinoma of the right upper back and localized CD4+ FMF (diagnosed June of 2017) of the right forearm presented in December of 2019 with a one-week history of new firm, pink plaques on the left medial upper arm and left buttock. The plaques were asymptomatic, non-tender, and non-pruritic. Punch biopsies were performed revealing a CD3, CD8, CD20 and beta-F1positive T-cell lymphoma, which was negative for CD30 and PAX5. To help distinguish between a progression to tumor-stage FMF versus a new diagnosis, T-cell receptor (TCR) gene rearrangements were investigated. Gene rearrangements were present in both beta and gamma genes, and these were divergent from those seen in the patient’s prior mycosis fungoides. Given these additional findings, a diagnosis of a distinct peripheral T cell lymphoma, not otherwise specified was most appropriate. Having a novel secondary lymphoma in a patient with mycosis fungoides is rare (<1.5%) making this situation unlikely and easily overlooked. T cell lymphoma with co-expression of CD20 makes this case all the more unusual.

Financial Disclosure:
No current or relevant financial relationships exist.