Pilomatrix Carcinoma in a Hodgkin Lymphoma Survivor: A Rare Second Primary Tumor.

Pilomatrix carcinoma is a rare, locally aggressive malignant adnexal tumor derived from hair follicle matrix cells. Although secondary malignancies are a well-known concern in Hodgkin lymphoma (HL) survivors, the occurrence of pilomatrix carcinoma in this setting is infrequent. We present the case of a 62-year-old man who was treated for Stage 1 Nodular Sclerosing Classical HL in 2018 with ABVD chemotherapy and radiotherapy. In January 2024, while in remission, he presented with a mass on the right posterior crus, distinct from the previous radiation field. Excision and histopathologic examination revealed pilomatrix carcinoma. Diagnosis was confirmed by immunohistochemistry, which showed a high Ki-67 index, nuclear beta-catenin positivity, and BerEP4 negativity. Owing to the aggressive nature of the tumor, wide re-excision and inguinal lymph node sampling were performed. This case report discusses the diagnostic challenges of this rare tumor and highlights its emergence as a second primary malignancy in a HL survivor, potentially linked to prior chemotherapy and systemic immune dysregulation.