Trichoblastoma is a rare benign tumor that arises from the germ cells of the hair follicle. The characteristic clinical presentation is a solitary, asymptomatic nodule on the face or scalp. Trichoblastoma may occur sporadically, in association with a hereditary disease, or within a nevus sebaceus. Trichoblastoma occurs most often in adults in their fifth and sixth decades, although it may be seen outside this age group. It affects males and females equally.

Trichoblastoma is closely related to trichoepithelioma, another benign follicular tumor that arises from follicular germ cells. Some experts consider trichoepithelioma to be a superficial variant of trichoblastoma; trichoepithelioma arises in the superficial dermis, and trichoblastoma arises in the deep dermis and subcutis.

Trichoblastoma is one of the most common tumors to arise within a nevus sebaceus, a congenital hamartoma most often found on the scalp. Trichoblastomas have been reported to occur in Curry-Jones syndrome (patchy hypopigmentation, polysyndactyly, cranial defects, and ophthalmic and gastrointestinal abnormalities).

Malignant transformation of trichoblastoma into a trichoblastic carcinoma, trichoblastic sarcoma, or trichoblastic carcinosarcoma is exceedingly rare. Malignant transformation most commonly presents as a long-standing lesion that suddenly enlarges. There is limited available data concerning the behavior and prognosis of malignant trichoblastic neoplasms; however, distant spread and death have been reported, and this aggressive behavior may be more common in sporadic cases.