Abstract
A proliferating trichilemmal tumor (PTT) is a rare, benign, exophytic tumor originating from the isthmus region of the outer root sheath of the hair follicle. Clinically, PTTs manifest as isolated, exophytic, firm nodules that have the potential to ulcerate. These tumors may occasionally originate from a pre-existing trichilemmal cyst, or they can emerge spontaneously. Most exclusively these lesions are seen on the scalp. However, rarely these tumors can be found in other anatomical areas. Our patient had a protruding mass in her shoulder for 20 years, and this is a rare site for the occurrence of these lesions; it could be the first case to document such a site, as far as we found in the literature. The mainstay treatment of the PTT is surgical excision of the tumor, assessing the histological margins to ensure sufficient resection was made, close monitoring, and follow-up with the patient.