Primary orbital melanoma has a similar genetic profile as other melanomas

This study analyzes the clinical, histologic and molecular genetic profiles of primary orbital melanoma.

Study design

The authors retrospectively reviewed 6 cases of primary orbital melanoma and correlated histopathologic, immunohistochemistry and PCR findings to the patients’ prognoses and clinical features. The study excluded patients with evidence of intraocular, conjunctival, skin/eyelid or nonconjunctival mucosal melanoma.

Outcomes

One case had oculodermal melanocytosis, while 3 cases had benign precursor lesions. Most tumors had a variable mixture of spindle and epitheliod melanoma cells, and were positive for the Melan A, HMB 45 and Sox 10 markers. All tumors were S100 positive and had chromosomal duplications or deletions. The most frequent chromosome duplications were 6p (5 cases), 8q (4 cases) and 17q (4 cases). Primary orbital melanoma tended to arise next to or within extraocular muscles.

Limitations

The authors speculate that the tumor’s proximity to the conjunctiva/anterior orbit might impart a conjunctival melanoma-like genetic profile, possibly mediated by light exposure. This is an interesting hypothesis but requires further study.  

Clinical significance

There may be two potential groups of primary orbital melanoma, including one associated with benign precursors. Patients with oculodermal melanocytosis who develop proptosis should undergo imaging studies to rule out orbital melanoma.