Researchers have identified eight risk factors to predict whether a choroidal nevus-a benign, flat, pigmented growth inside the eye and beneath the retina-may develop into melanoma.
The team of researchers were from Thomas Jefferson University, U.S.
"There is strong interest for early detection of choroidal melanoma [a malignant growth], and its differentiation from nevus continues to be the major impediment," the authors write as background information in an article describing their study, published in the Archives of Ophthalmology, one of the JAMA/Archives journals.
Benign choroidal nevi and small melanomas share many characteristics, including colour, location and size.
"The challenge is to identify the single small melanoma among the thousands of choroidal nevi. It has been estimated that 6 percent of the white population harbors a choroidal nevus and that one in approximately 8,000 of these nevi transform into melanoma," the authors write.
Dr. Carol L. Shields and colleagues at Wills Eye Institute in Philadelphia studied the medical records of 2,514 consecutive eyes of patients with choroidal nevi between 1974 and 2006.
The researchers say that the tumours had a median (midpoint) diameter of 5 millimetres, and a median thickness of 1.5 millimetres, at the beginning of the study.
Choroidal nevi grew into melanoma in a total of 180 eyes (7 percent) over an average follow-up of 53 months, including 2 percent after one year, 9 percent after five years and 13 percent after ten years.
According to the researchers, the factors that predicted growth into melanoma included five previously identified factors: tumour thickness greater than 2 millimetres, fluid beneath the retina, symptoms such as decreased vision or flashes and floaters, orange pigment and a tumour edge within 3 millimetres of the optic disc.
They said that the research team identified two new factors: hollowness of the growth on ultrasound and the absence of a surrounding halo, or circular band of depigmentation.
"Until systemic therapies for metastastic uveal melanoma improve, our focus should be on early detection to minimize metastastic disease. All ophthalmologists should participate in this effort and patients with risk factors can be referred for evaluation at centers familiar with the nuances in the diagnosis and management of early melanoma," the authors write.
Based on their findings, the researchers came to the conclusion that choroidal nevi patients who do not display any of the seven features of disease should be monitored twice yearly at first, and then followed up yearly if their condition remains stable.
They also said that those with one or two features should be monitored every four to six months; and those with three or more features should be evaluated at an experienced centre for possible treatment.