Multiplex fluorescence in situ hybridization identifies novel rearrangements of chromosomes 6, 15, and 18 in primary uveal melanoma

Uveal melanomas are the commonest ocular tumour of adults and are characterized by reproducible alterations of chromosomes 1, 3, 6 and 8. These alterations are of prognostic relevance and have also be shown to correlate to high risk and low risk metastatic categories of uveal melanoma as defined by micro-array analysis. It is, however, possible that a catalogue of relevant genetic alterations, involving gene rearrangement rather than amplification, have as yet eluded identification. To address this point we examined 14 primary uveal melanomas, using 24 colour multiplex fluorescence in situ hybridization (M-FISH). All tumours were karyotyped following G-Banding, and M-FISH was performed to confirm and clarify the identity of abnormal chromosomes. M-FISH data were obtained from all tumours and was able to establish the nature of most abnormalities not fully characterized by cytogenetics. Abnormalities of chromosome 6 were far more frequent than previously indicated, in approximately 70% of cases, indicating they have been substantially underrepresented in past studies of uveal melanoma. Spindle melanomas were found to have novel rearrangements affecting in particular chromosomes 6, 15 and 18, suggesting that juxtaposition of genes through translocational events may play a role in the development of some uveal melanomas. In conclusion, this study is the largest of primary uveal melanoma analysed by M-FISH and indicates that alterations of chromosome 6 have previously been underestimated. Furthermore spindle melanomas are prone to rearrangements affecting chromosomes 6, 15 and 18, which may relate to early changes in uveal melanoma development or associate with those melanomas of a more differentiated status.