Abstract

A 66-year-old female presented with six months of rapid growth and tenderness of a 3 cm firm pink nodule on the vertex scalp, previously stable in size for 15 years. Excisional biopsy showed an unremarkable epidermis and a large lobulated dermal proliferation composed mostly of mature epithelioid cells with high grade atypia, squamous eddies, and trichilemmal differentiation with several foci within the stroma of markedly pleomorphic spindled and multinucleated cells with high mitotic rate. Extensive necrosis, atypical mitoses, and fibroplasia were also noted. The invasive, atypical epithelial component stained positive for AE1/AE3, p63, and p40. The spindled component stained positive for vimentin and CD10. A diagnosis of malignant proliferating trichilemmal tumor (MPTT) with carcinosarcoma transformation was made. PET/CT showed mildly hypermetabolic left-sided parotid and cervical lymph nodes. The patient underwent Mohs surgery followed by wide local excision and left-sided neck dissection and superficial parotidectomy. There was no residual tumor or lymph node involvement, and no adjuvant radiation or therapy was pursued. No recurrence was seen at 4 months. Carcinosarcoma is a rare biphasic dermal tumor with both epithelial and mesenchymal components. The majority of cutaneous carcinosarcomas are associated with basal cell, squamous cell, or adnexal carcinomas. MPTT are rare tumors arising in a pilar tumor or proliferating trichilemmal cyst, with some exhibiting nodal or distant metastasis. A malignant spindle cell component arising within a proliferating trichilemmal tumor is a rare neoplasm with a range of clinical behavior. There are 4 cases of MPTT with sarcomatous transformation in the literature. However, none showed a prominent atypical carcinomatous component. We present the first case of MPTT with transition to both highly atypical spindle cell and epithelioid components to highlight this rare entity and the challenges in its prognosis and management.

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