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%), and in 10 patients (47.5%) 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%) of 21 patients. Of these eight patients, there were liver metastases in seven (88%) and brain metastases in one (12%). 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.
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