EVects of proton beam irradiation on uveal melanomas: a comparative study of Ki-67 expression in irradiated versus non-irradiated melanomas

Aims—To assess the cellular proliferation using the monoclonal antibody Ki-67, in paraYn embedded uveal melanomas irradiated by proton beam, as well as in non-irradiated uveal melanomas. Methods—30 enucleated eyes were included for histopathological study and Ki-67 immunostaining. Patients were enucleated between 1991 and 1996 for uveal melanoma, 14 after proton beam irradiation and 16 without treatment (control group). The mean follow up period was 2.5 years after diagnosis and 1 year after enucleation. Results—A significant relation was found between Ki-67 score and mitotic index (r = 0.56, p = 0.001), histological largest tumour diameter (r = 0.38, p = 0.03), fibrosis (r = −0.35, p = 0.05), absence of tumoral pigmentation (p = 0.05), and presence of vascular thrombosis (p = 0.03). The Ki-67 score was significantly higher in the non-irradiated group (p = 0.01) and in the group of patients whose cause of enucleation was tumoral evolution (p = 0.005) compared with the group of patients enucleated after neovascular glaucoma. The Ki-67 score was very high in a case of orbital recurrence of uveal melanoma and metastatic death. 70% of metastasised tumours showed a Ki-67 score higher than the median value. Conclusion—Ki-67 labelling is a reliable method of estimating the proliferative activity in uveal melanomas after proton beam irradiation. The Ki-67 score is significantly correlated with prognostic variables (mitotic index and histological largest tumour diameter), and with radiation eVects after proton beam irradiation. (Br J Ophthalmol 2000;84:98–102) Uveal melanoma is the most common primary adult ocular malignancy with an incidence of 0.6 cases/100 000 inhabitants. Their high ability to produce metastases is well recognised. Proton beam irradiation is currently used in the treatment of choroidal and ciliary body melanomas to destroy the tumour while preserving some vision and retaining the globe. The histological variables and the proliferation markers that predict the outcome of patients with uveal melanoma in terms of metastatic disease and tumour related death have been previously explored, using variance in nucleolar area, 3 inverse standard deviation of the nucleolar area, 4 mitotic index, 6 DNA or RNA ploidy status, bromodeoxyuridine labelling, 12 and PCNA immunostaining. 13 14 With the development of the proliferation associated monoclonal antibody Ki-67 by Gerdes et al in 1983, identification of cells in mid-G1 (first gap), S (DNA synthesis), G2 (second gap), and M (mitosis) phases of the cell cycle on tissue sections has become possible. Growth fraction assessed with Ki-67 is reported as an independent prognostic marker in several tumours, such as nonHodgkin’s lymphomas, gliomas, soft tissue tumours, and non-irradiated uveal melanomas. The cellular proliferation of uveal melanoma after brachytherapy has been previously studied. 13 19–21 However, to our knowledge, the proliferation rate of uveal melanoma treated by proton beam irradiation has not been described using Ki-67 immunostaining. Since radiation induced damage within tumours seems to be responsible for tumour cell death and sterilisation of uveal melanoma cells, an immunohistochemical study using Ki-67 antigen detection appears to be an attractive approach to analyse the eVects of proton beam irradiation on uveal melanomas. The purpose of the current study was to compare the proliferation rate of uveal melanomas irradiated by charged particles of proton with that of non-irradiated melanomas using immunohistochemical staining with a monoclonal antibody against Ki-67, and to correlate Ki-67 score with conventional clinical and pathological prognostic variables. Patients and methods Forty consecutive patients with uveal melanoma underwent enucleation between 1991 and 1996, either without adjunct therapy (17 patients) or after proton beam irradiation (23 patients). Proton beam irradiation (60 Gy) had been used in the treatment of uveal melanomas for 198 patients at the Nice Biomedical Cyclotron between June 1991 and August 1996. In the control group, eyes were enucleated if the tumour size was excessive (maximum tumour height >10 mm) or in the case of neovascular glaucoma. In the irradiated group, enucleation was performed in cases of continued tumour growth or tumour recurBr J Ophthalmol 2000;84:98–102 98 Department of Ophthalmology, Croix-Rousse Hospital, University of Lyons, France