A Case of Proliferating Trichilemmal Tumor Occurred on the Right Forearm

Abstract

A 45-year-old woman presented with a subcutaneous nodule on her right forearm that had developed 20 years earlier. Physical examination revealed a brownish subcutaneous nodule of 15 mm in diameter on the right forearm. The subcutaneous nodule was resected and histologically diagnosed as proliferating trichilemmal tumor (PTT). PTT is a rare skin tumor that is more common in women than in men. More than 90% of PTT lesions arise on the scalp. Herein, we report a rare case of PTT on the right forearm. Although most PTTs are benign, there is a possibility of recurrence or malignant transformation ; thus, some researchers consider PTT as a malignancy. The mechanism of pathogenesis and malignant transformation of PTT remains to be elucidated. Further accumulation of data on PTT is needed to elucidate its pathogenesis and create clear guidelines for treatment. Skin Research, 24 : 182-186, 2025