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.
Practice Points
- Glomus tumors have been subdivided into 3 groups with different prognoses.
- The term glomus tumor of uncertain malignant potential (GTUMP) was introduced to describe glomus tumors that demonstrate marked nuclear atypia but do not fulfill histologic criteria for malignancy.
- Complete excision with negative margins is always necessary in cases of GTUMPs.
Distinction between malignant GTs and GTUMPs in the presence of unusual histologic features may be difficult.12 Glomus tumors that do not fulfill criteria for malignancy but have at least 1 atypical feature other than nuclear pleomorphism should be named GTUMPs. According to classification criteria, a true malignant GT is a highly aggressive tumor with metastatic potential. In a case series reported by Folpe et al,2 38% (20/52) of malignant GTs showed metastases, while metastatic disease was not observed in the tumors classified as GTUMPs. Wide surgical excision or Mohs micrographic surgery13 are the treatments of choice for malignant GTs and GTUMPs. Complete excision of the lesion with negative margins is always necessary in cases of GTUMPs. After the diagnosis of GTUMP, adequate follow-up should berecommended due to the possibility of local recurrence or distant metastasis.
Conclusion
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.
