Proliferating epithelial cysts. Clinicopathological analysis of 96 cases.

Ninety-six proliferating cutaneous epithelial cysts were classified into two subtypes, proliferating trichilemmal cysts (PTC) and proliferating epidermoid cysts (PEC), depending on the mode of keratinization or the origin of the tumors. The clinicopathological features and the biological behavior of these two subtypes were compared. Among 63 patients with PTC, 45 (71%) were women and 18 (29%) were men. The most common site was the scalp (78%), followed by the trunk (13%). These tumors were well circumscribed subepidermal lesions and demonstrated uniform histologic pattern with varying degrees of cytologic atypia. A few tumors extended into the epidermis and occasionally became ulcerated. Follow-up of 59 (94%) PTC for an average of 4 years revealed recurrence in one. Ten tumors demonstrated carcinomatous changes including one with anaplastic carcinoma and regional lymph node metastasis. None of these tumors recurred or developed further metastasis following wide excision. Of 33 PECs, 12 (36%) occurred in women and 21 (64%) in men. These tumors were widely distributed in the pelvic and anogenital areas (36%), followed by the scalp (21%), upper extremities (18%), and trunk (15%). Seventy-nine percent of the PECs were located in areas outside the scalp. The PECs were subepidermal tumors but often communicated to the surface. The histologic pattern of PEC was more variable than that of PTC. Seven tumors exhibited carcinomatous changes. Follow-up of 30 (91%) PEC revealed local recurrences in 6, with multiple recurrences in 3, and extensive local invasion in 2, resulting in death in one. Greater anaplasia, high mitotic rate and deeper invasion were associated with increased incidence of recurrence and aggressive behavior. Although both PTC and PEC were locally aggressive tumors and potentially malignant, distant metastasis was unusual. These tumors should be treated with wide local excision, especially those showing cytologic atypia and carcinomatous changes.