Tumor of the follicular infundibulum: an epidermal reaction pattern?

Our recent experience indicates that the desmoplastic variant of tumor of the follicular infundibulum (TFI) is not, as previously believed, entirely uncommon. To clarify the defining clinical and microscopic features of TFI with special relevance to the histologic variants, we retrospectively reviewed cases with a histologic diagnosis of TFI between 1999 and 2008. Of the 74 cases retrieved, 53 TFI cases in 50 patients were identified with an incidence approximating 17 per 100,000. Clinically, TFI seems to be slightly more common in men (52% vs. 48%) and more common on the head and neck (around 77%) and presents as plaques (approximately 47%) and as multiple lesions (6%). Histologically, the majority showed classic features of a horizontal plate-like proliferation of large, bland-appearing, pale epithelial cells. Other features included an eosinophilic cuticle (70%), ductal differentiation (45%), cornoid lamellae (17%), and desmoplasia (11%). Of interest, approximately one fourth (25%) were associated with other cutaneous lesions, which included basal cell carcinoma, actinic keratosis, desmoplastic malignant melanoma, junctional melanocytic nevus, tricholemmoma, and epidermal inclusion cyst. In addition to expanding the constellation of the clinical and histopathologic findings, the increased association with other cutaneous lesions in the current study suggests that TFI may represent an epidermal reaction pattern.