Pilomatrix Carcinoma Arising From a Previously Excised Giant Pilomatrixoma: A Case Report

A 49‐year‐old male presented with a giant pilomatrixoma in the arm that underwent malignant transformation into pilomatrix carcinoma. The patient originally presented with a malaise and back pain. Workup revealed anemia and hypocalcemia from chronic tumor drainage, and a 20‐cm giant pilomatrixoma with fungation, requiring wide resection. Subsequent marginal recurrence with malignant transformation was managed through wide resection and radiation, resulting in no evidence of disease 2 years postoperatively. This case represents one of the few documented cases of malignant transformation of a lesion that is thought to be largely benign. It underscores the diagnostic challenges of giant pilomatrixomas, emphasizing the potential for malignant transformation. Takeaways include a vigilant approach to long‐standing masses, prompt diagnosis, multidisciplinary management, and appropriate surveillance. This case highlights the need for heightened diagnostic vigilance and long‐term surveillance of large or long‐standing pilomatrix lesions due to malignant potential.