Multiple tumors of follicular infundibulum with sweat duct differentiation.

A 67-year-old man is reported with multiple tumors of follicular infundibulum containing ducts. Approximately 30 hypopigmented, scaling macules and minimally elevated papules were present on the face. Skin biopsy specimens from 5 representative lesions revealed similar findings. There was a proliferation of ramifying strands of pale-staining keratinocytes in the upper dermis showing connections with follicular infundibula of vellus follicles and epidermis. There was evidence of hair follicle differentiation with small follicular bulbs, papillary mesenchymal bodies, keratocysts, and occasional hair shafts in the tumor. These findings are characteristic of prior reports of TFI. Ducts were also present within the epithelial cords. Carcinoembryonic antigen, gross cystic disease fluid protein-15, epithelial membrane antigen, and S-100 protein were identified within the tumor. We theorize that the ductal elements within these TFI reflect the multipotential differentiating capacity of portions of infundibular epithelium.