Tumor‐stage mycosis fungoides in palmoplantar localization with large‐cell transformation and partial CD30 expression shows complete response to brentuximab vedotin

Mycosis fungoides in palmoplantar localization (MFPP) is a rare variant of MF that is confined to the hands and feet. Patients commonly receive treatment over many years for suspected palmoplantar dermatitis before the diagnosis is made. Most MFPP patients remain at patch or plaque stage, and often respond to treatment with radiotherapy. Herein, we describe a 77‐year‐old man who suffered 6 years of hand and foot dermatitis that failed multiple treatments, most notably TNF‐α inhibitors and mycophenolate mofetil. He eventually developed a tumor on the hand, which was biopsied to reveal a dense dermal infiltrate of large lymphocytes (CD3+/CD4‐/CD8‐/TCR‐BetaF1+/partial CD30+). A subsequent biopsy of an eczematous patch from his hand revealed an epidermotropic and syringotropic infiltrate comprised of smaller lymphocytes with a concordant immunophenotype and matching clonal peak with TCR gene rearrangement. He was diagnosed with MFPP and started on radiotherapy with a modest response; therefore, a decision was made to start brentuximab vedotin, which resulted in a complete response. MFPP is an exceedingly rare variant of MF that can show large‐cell transformation and progress in stage. We highlight a possible association between disease progression and immunosuppressants and the potential role for treatment with brentuximab.