Iris nevi have ‘low’ malignant potential

By Joanna Lyford, Senior medwireNews Reporter

The malignant transformation rate for iris nevi is 8% over 15 years, a case series by US researchers has found.

The team also identified risk factors for malignant transformation that can be remembered using the "ABCDEF" mnemonic, representing young Age, Blood (hyphema), Clock hour inferior, Diffuse (involving entire iris surface) configuration, Ectropion uveae, and Feathery margins.

"Patients with these clinical features should have periodic monitoring for documentation of tumor growth and appropriate management," write Carol Shields (Wills Eye Institute, Philadelphia, Pennsylvania) and co-authors in Ophthalmology.

Shields' team undertook a retrospective analysis of 1611 consecutive patients referred to an ocular oncology center with iris nevi. The patients' mean age was 54 years, 39% were male, 97% were White, and 4% had a history of skin melanoma.

The mean follow-up period was 68 months (range 3-465 months). During this time, iris nevi transformation into iris melanoma occurred in 27 patients, or 2% of the cohort. Kaplan-Meier estimates of transformation rates were 2.6% at 5 years, 4.1% at 10 years, 7.5% at 15 years, and 11.2% at 20 years.

Among the 27 patients with melanoma, nevi grew by an average of 1.7 mm in basal diameter and 1.0 mm in thickness. The mean growth rate was 0.6 mm/year (22%/year) in diameter and 0.3 mm/year (62%/year) in thickness.

Patients with malignant transformation tended to be significantly younger than those without (39 vs 52 years) and were more likely to have blue irises (78 vs 51%).

Multivariable analysis identified six factors that significantly predicted malignant transformation: age 40 years or less at presentation (48 vs 24%; hazard ratio [HR]=3); hyphema (11 vs <1%; HR=9); 4:00 to 9:00 clock-hour tumor location (96 vs 75%; HR=9); diffuse tumor involving entire iris surface (4 vs <1%; HR=14); ectropion uveae (48 vs 18%; HR=4); and feathery tumor margins (52 vs 25%; HR=3).

The most frequent treatment for melanoma was surgical iridectomy (n=17), while other strategies were plaque radiotherapy (n=8) and enucleation (n=2).

Shields and colleagues say that iris melanoma, while rare, is clinically important because it can necessitate enucleation and lead to metastatic disease. Furthermore, iris nevi can also serve as a marker for a predisposed phenotype at risk for uveal melanoma.

They conclude that "iris nevus carries a low risk for growth into melanoma. Factors predictive of growth can be remembered by the ABCDEF guide representing Age young, Blood (hyphema), Clock hour inferior, Diffuse (involving entire iris surface) configuration, Ectropion uveae, Feathery margins."

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