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INDIANA ASSOCIATION OF PATHOLOGISTS


Register now | 2019 IAP Fall CME Meeting | October 26 

Anti-microbial Susceptibility Testing | Testicular Germ Cell Tumors | Sarcoma | EGFR Mutations


Final Diagnosis: Atypical glomus cell proliferation (glomus tumor of uncertain malignant potential)

Discussion: Glomus tumors are a rare entity, thought to compromise approximately 1.6% of all soft tissue tumors.1 They most commonly occur in the distal extremities, but tumors have been reported in almost every anatomical location.2 Glomus tumors predominately occur in the skin and subcutaneous tissue.2 Although the vast majority of glomus tumors are benign, they may rarely be classified as atypical or malignant.3

The WHO currently recognizes three categories of glomus tumors: glomus tumor, glomus tumor of uncertain malignant potential, and malignant glomus tumor. According to the WHO, the diagnosis of malignant glomus tumor should be rendered when the tumor demonstrates marked nuclear atypia and any level of mitotic activity, or atypical mitotic figures.2 Tumors that demonstrate features more concerning than those of a normal glomus tumor, yet fail to fulfill the criteria of malignant glomus tumor, should be classified as glomus tumor of uncertain malignant potential.1

The WHO additionally notes that glomus tumors greater than two centimeters in size should be considered to have “uncertain malignant potential.” Malignant glomus tumors may resemble leiomyosarcoma, fibrosarcoma, or may consist of sheets of malignant appearing round cells. Given their origin as modified smooth muscle cells, glomus cells will demonstrate positivity for immunohistochemical makers such as SMA and calponin, and have abundant pericellular production of type IV collagen. Glomus tumors may be familial, and often show autosomal dominant inheritance through inactivating mutations in the glomin gene (GLMN). Benign glomus tumors are cured by resection and have an excellent prognosis; however, malignant glomus tumors are aggressive with high metastatic potential, resulting in metastasis or and death in 40% of patients.2 In general, glomus tumors of uncertain malignant potential are thought to behave similar to benign glomus tumors, although metastasis and aggressive behavior have rarely been seen.1

The diagnosis of glomus tumor of uncertain malignant potential warrants close clinical follow-up. In our case, given the size of the specimen, slightly larger cells, and increased mitotic activity plus the absence of severe cytologic atypia and atypical mitotic figures, the diagnosis of glomus tumor of uncertain malignant potential was made. Fragmentation of the specimen made assessment of the margin status suboptimal; therefore, complete excision to allow for full pathologic examination was recommended.

References

1. Binesh F, Akhavan A, Zahir ST, Bovanlu TR. Clinically malignant atypical glomus tumour. BMJ Case Rep. 2013;2013:bcr2012007618.

2. WHO classification of tumours of soft tissue and bone. In: Fletcher CDM, ed. 4th ed. ed. Lyon :: IARC Press; 2013.

3. Goldblum JR. Enzinger and Weiss's soft tissue tumors. In: Folpe AL, Weiss SW, Enzinger FM, Weiss SW, eds. 6th ed. ed. Philadelphia, PA :: Saunders/Elsevier; 2014.



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