Abstract

A 58-year-old male with no significant past medical history, presented to the Emergency Department due to uncontrolled bleeding of a large, cutaneous tumor, secondary to trauma. On physical examination, a multi-lobulated, exophytic mass with laceration was identified on his mid central back. Reportedly, the tumor was present for several years and was enlarging slowly. Imaging was performed and revealed a large subcutaneous mass abutting the paraspinal muscles.  

The tumor was surgically excised with wide margins. The tissue specimen consisted of an 18.2 x 12 cm skin ellipse containing a 12 x 11.3 x 4.4 cm gray-tan, nodular, exophytic lesion. Sectioning of the lesion revealed a tan-white, solid and cystic cut surface, filled with tan-white, friable material. 

Histologically, the tissue sections showed a malignant lesion, composed of proliferative keratinocytes infiltrating the surrounding subcutaneous tissue with areas of necrosis. The cells exhibited significant nuclear atypia, cellular pleomorphism, dyskeratosis, and karyorrhexis with increased mitotic figures.  Additionally, areas of the cystic epithelium show stratified squamous lining without an accompanying granular layer, surrounding compact keratinous material. These findings were most consistent with a malignant proliferating pilar tumor (MPPT) arising from a proliferating pilar tumor. 

Malignant proliferating pilar tumor is a rare adnexal tumor that represents the malignant counterpart of the trichilemmal spectrum, which encompasses pilar and proliferating pilar tumors. MPPT can arise de novo or in a pre-existing pilar cyst.