Correlation of heterogeneity for chromosome 3 copy number with cell type in choroidal melanoma of mixed-cell type.

PURPOSE: To study heterogeneity for chromosome 3 copy number in mixed choroidal melanoma with discrete populations of spindle and epithelioid cells using chromosome in situ hybridization (CISH) and to correlate chromosomal loss with cell type. METHODS: Twenty-two archival cases of choroidal melanoma with discrete populations of spindle and epithelioid cells were identified. CISH was used to identify chromosome 3 copy number in spindle and epithelioid areas. RESULTS: Monosomy 3 was detected in 12 (55%) of 22 choroidal melanomas. Of these, 10 (45%) had two copies of chromosome 3 in both epithelioid and spindle cells, 7 (32%) showed monosomy 3 in the epithelioid areas only, and 5 (23%) showed monosomy 3 in both epithelioid and spindle areas. CONCLUSIONS: CISH is a useful technique for analyzing chromosome copy number in different cell populations within a tumor. In mixed choroidal melanomas with discrete spindle and epithelioid cell populations, there may be heterogeneity for chromosome 3 copy number that correlates with areas of different cell type.