Malignant Proliferating Trichilemmal Tumor of the Scalp Treated With Excision and Adjuvant Radiotherapy.

Proliferating trichilemmal cysts are common benign lesions, but their malignant counterpart, malignant proliferating trichilemmal tumor (MPTT), is an extremely rare adnexal malignancy that predominantly arises on the scalp. Due to clinical and histological overlap, it is frequently misdiagnosed as squamous cell carcinoma. We report the case of a 70-year-old woman who presented with a progressively enlarging, painless, and bleeding midline scalp mass evolving over one year. A craniofacial CT scan (SOMATOM, Siemens Healthineers, Erlangen, Germany) revealed a well-defined, heterogeneous soft-tissue lesion measuring 75 × 55 mm without underlying bone lysis. Systemic staging showed no distant metastases. An initial incisional biopsy suggested squamous cell carcinoma. The patient underwent wide surgical excision with 1-cm safety margins and deep periosteal bed re-excision. Tension-free primary closure was achieved following extensive scalp undermining and galeal scoring. Definitive histopathological and immunohistochemical examination confirmed MPTT with clear margins. Due to the tumor size and high mitotic rate, the patient received adjuvant hypofractionated Volumetric Modulated Arc Therapy (VMAT; Elekta AB, Stockholm, Sweden), delivering 45 Gy in 10 fractions, resulting in a favorable clinical outcome without recurrence at six months of follow-up. While short-term results demonstrate a favorable outcome, extended surveillance is mandatory due to the potential for late recurrence or metastasis. This case highlights the critical importance of accurate clinical, radiological, and especially histopathological diagnosis using immunohistochemistry to differentiate MPTT from squamous cell carcinoma, ensuring optimal surgical margins and appropriate adjuvant management.