Aims: To analyse the distribution of posterior uveal melanoma origin sites and to visualise the patterns of tumour extent in the ocular fundus.
Methods: Data on the size and location of 110 posterior uveal melanomas were converted into a database of two-dimensional retinal charts by means of computer-drawing software. The initiation sites (geometric tumour centres) were entered into corresponding sectors of the retinal chart. The extent of the tumours was visualised by merging the charts and displaying the number of overlapping tumours on colour-coded contour maps.
Results: Seventy-one initiation sites (65%) were located in the temporal and 39 (35%) in the nasal hemisphere (p = 0.002). Seventy-six initiation sites (69%) were located posterior and 34 (31%) anterior to the equator. More initiation sites anterior to the equator were observed in large versus small/medium tumours (p = 0.0003), in tumours with a largest basal diameter/height ratio <2 versus ⩾2 (p = 0.002), in tumours with a ruptured versus intact Bruch membrane (p = 0.03), in tumours with a mixed/epithelioid versus spindle cell type (p = 0.02) and in tumours leading to metastatic disease (p = 0.003).
Conclusion: The temporal hemisphere posterior to the equator is the preferential area of melanoma occurrence and growth. For larger and more aggressive tumours, there is a shift towards more peripherally located initiation sites.
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Funding: The study was supported by grants from The Norwegian Cancer Society.
Competing interests: None.
Ethics approval: The study was approved by The Norwegian Social Science Data Services, and followed the ethical standards for clinical research in accordance with the Helsinki Declaration.