Growth rate of indeterminate choroidal lesions prior to melanoma diagnosis

Small choroidal melanocytic lesions have a low rate of metastasis and can be reasonably managed with surveillance until they demonstrate evidence of growth or clinical risk factors for melanoma. However, even choroidal nevi are not stationary, with many exhibiting slow growth over time. We sought to quantify the growth rates of indeterminate choroidal lesions that were initially observed prior to a clinical diagnosis of melanoma.

A single-center retrospective study was performed of patients diagnosed with choroidal melanoma based upon clinical characteristics who were initially followed for indeterminate lesions over at least 6 months. Subjects were included if they had a minimum of two B-scan ultrasound measurements prior to the visit at which melanoma was diagnosed. Demographic and tumor characteristics were collected from the medical record. Growth rates were calculated as the change in lesion thickness in mm per month and were recorded at 6-month intervals; ultrasound measurements less than 1 month apart were excluded. The characteristics of indeterminate lesions with faster versus slower growth rates prior to melanoma diagnosis were compared.

Fifty-four patients met inclusion criteria. The mean age at melanoma diagnosis was 67.4 years, and 53.7% were female. Subjects had a median of four B-scan ultrasound measurements prior to melanoma diagnosis (range 2-19) and were followed for a median of 40.6 months (range 9.9-138.0 months). The mean lesion thickness was 1.4 mm (range 0.5-2.2 mm) at presentation, and increased to 2.3 mm (range 1.5-5.7 mm) at melanoma diagnosis. The mean growth rate did not exceed 0.021 mm/month (95% CI: 0.004-0.039; equivalent to 0.25 mm/year) for indeterminate lesions, but increased to 0.057 mm/month (95% CI: 0.043-0.071 mm/month; equivalent to 0.68 mm/year) at the time of melanoma diagnosis. Rapidly growing lesions had a greater tumor thickness and shorter duration of observation at the time of melanoma diagnosis.

For most indeterminate choroidal lesions eventually diagnosed as melanoma, the lesion thickness was relatively stable for a period of time, then rose significantly between the penultimate visit and the final visit. These findings confirm the recommendation for continued monitoring of suspicious choroidal lesions, as the growth rate may accelerate just prior to melanoma diagnosis. Lesions with a mean growth rate of up to 0.25 mm/year were observed, whereas lesions clinically determined to have transformed into melanoma demonstrated a mean growth rate of 0.68 mm/year. These values provide a baseline for future studies and potential therapies directed at stabilizing or reducing the growth of indeterminate choroidal lesions or small choroidal melanomas. Limitations of this study include its retrospective nature and reliance on clinical diagnostic criteria.