Proliferating trichilemmal tumor with a malignant spindle cell component

Proliferating trichilemmal tumors (PTTs) are uncommon exuberant growths of cells derived from the external root sheath. They tend to occur in older women, with a predilection for the scalp. Resection is usually curative. Spindle cell components arising within PTTs are exceedingly rare, with only three known cases previously reported. Of these three cases, one patient died from widespread metastasis.

Histological and immunohistochemical examinations were performed on a tumor from a 54-year-old man which, after exhibiting slow growth for 3 years, increased rapidly in size.

Microscopic examination revealed cystic lobules of squamous cells without a granular cell layer surrounding amorphous eosinophilic debris within the dermis. Also present was a poorly circumscribed focus of spindle cells with hyperchromasia, pleomorphism, giant cells, and abundant mitoses, including abnormal forms. Immunohistochemistry showed the spindle cells to stain positively for vimentin, but negatively for keratin, epithelial membrane antigen and S-100 antibodies.

A malignant spindle cell component arising within a PTT is a rare neoplasm which has been associated with death from widespread metastasis.