PLE-2201

A 55-year-old man presents with a chronic rash over the buttocks and hips that has been unresponsive to topical steroids. It has recently started to itch. Examination shows 6- to 12-cm erythematous, scaling plaques in a bathing trunk distribution. Potassium hydroxide preparation is negative for evidence of a fungal infection. A skin biopsy indicates an atypical lymphocytic infiltrate with evidence of epidermotropism and Pautrier microabscess formation. What is the most likely diagnosis?