Follicular Neoplasms

Follicular tumors are one form of “adnexal tumors.” The adnexa in dermatopathology are skin appendages: the hair follicles, sebaceous glands, and sweat glands. In gynecologic pathology, the adnexa are fallopian tubes and ovaries. Follicular, sebaceous and sweat gland tumors are not necessarily derived from such structures; we prefer to think that immature pluripotential cells demonstrate “differentiation toward” hair follicles, sebaceous glands, or sweat glands. It is quite common for some tumors to produce various combinations of hair follicle, sebaceous, and sweat ductal structures, all in the same tumor, making our artificial classification schemes oversimplified. Adnexal tumors are like snowflakes; many unusual unclassifiable variants are sometimes found. It is a fertile ground for “lumper-splitter” wars, where authorities often rename and reclassify tumors, and they argue about whether a neoplasm is a new entity or merely a variant of another tumor. Terminology varies according to the author.