Glomus tumor of uncertain malignant potential on the forehead.

Malignant glomus tumors (GTs) are rare, and diagnosis requires consideration of specific histologic criteria. Glomus tumors that do not fulfill the histologic criteria for malignancy but show at least 1 feature other than nuclear atypia should be classified as GTs of uncertain malignant potential (GTUMPs). We report the case of a 74-year-old man with a slowly progressing, painful, 2.5-cm nodule on the forehead that was successfully treated via wide surgical excision and was later diagnosed as a GTUMP. Three-year follow-up showed no local recurrence or distant metastasis. Malignant GTs and GTUMPs are rare, and the nomenclature and classification of these tumors is controversial. These findings and the difficulty of differential diagnosis in a continuum between benignity and malignancy prompted our report.