Aggressive Form of Mycosis Fungoides With Bilateral Testicular Involvement and Salivary Gland Mass, Exhibiting Phenotypic Switch.

We report the case of a 72-year-old man with bilateral testicular involvement by mycosis fungoides (MF). The patient was diagnosed with MF 6 months prior, and testicular involvement was found upon staging. The rare behavior of MF, with early visceral involvement and no hematolymphoid organs affected, had a poor prognosis with patient death 14 months after the original diagnosis despite surgery and chemotherapy. The neoplastic cells showed a phenotypic switch from a CD4 + /CD8 - profile in the skin to a CD4 - /CD8 - in the testis and the same clone, confirmed with T-cell receptor gene rearrangement studies, making this the third reported case of MF affecting the testis and the first with clonality studies to confirm it. The clinical evolution may be related to its distinctive biology showcased in the neoplastic cell's switch to a more aggressive CD4 - /CD8 - profile and the early extension of the disease to an uncommon visceral site.