Purpose: Primary orbital melanomas are rare tumors with a poorly defined biologic course. Most recorded experiences concern single case reports. The authors evaluated the applicability of several of the histopathologic prognostic indicators used for uveal melanomas to a series of primary orbital melanomas with known clinical follow-up.
Methods: Twenty-one primary orbital melanomas, each with at least a 1-year follow-up after diagnosis, were evaluated for (1) modified Callender cell type, (2) mitotic count per 40 high-power fields, (3) lymphocyte count (less than versus greater than 100/20 high-power fields), (4) blue nevus component, and (5) largest tumor diameter.
Results: All patients for whom race was recorded were white. The mean age at diagnosis was 42 years (range, 15-84 years). There was an associated blue nevus in 19 patients (90 percent), and in 10 patients (47.5 percent) there was some form of congenital melanosis. With a mean follow-up period of 4.5 years (range, 1-13 years), mortality from metastatic tumor occurred in 8 (38 percent) of 21 patients. Of these eight patients, there were liver metastases in seven (88 percent) and brain metastases in one (12 percent). Indicators of poor prognosis were tumors of mixed cell type with high mitotic count and greater patient age with underlying congenital melanosis.
Conclusion: Most primary orbital melanomas occur in white patients and are associated with blue nevi. These tumors are similar to uveal melanomas with respect to prognostic indicators and pattern of metastasis.