The Value of Ultrasound as a Tool to Evaluate Uveal Melanoma in a Rabbit Model

Abstract

Abstract: : Purpose: Ophthalmic ultrasound has become an essential clinical tool in the diagnosis of uveal melanoma. To the best of our knowledge, ocular ultrasound has never been used to evaluate uveal melanoma in an experimental model. The aim of this study is to test ultrasound as a method of determining the final dimensions of tumors obtained from two human uveal melanoma cell lines of different metastatic potential. Methods: Two groups of fifteen immunosuppressed New Zealand albino rabbits were injected with 1x10⁶ total cells into the suprachoroidal space with either the MKT-BR (low metastatic potential) or 92.1 (high metastatic potential) human melanoma cell line. Ten animals of the MKT-BR group and fourteen animals of the 92.1 group were used in this study. Ultrasound images, using an Ophthascan-s with a 10 MHz B-scan probe, were obtained during the last week of the 8-week animal model. All animals were under anaesthesia for the ultrasound test. Tumor size and location were determined by longitudinal and transverse sections. The thickness of the tumor was also measured. Involvement of the ciliary body and presence of multiple foci were evaluated. Animals were euthanised at the end of the 8-week experiment. The enucleated eyes were submitted to histopathological (H&E) and immunohistochemical evaluation (HMB-45). Results: No statistically significant differences in the average tumor dimensions were found between the two groups: tumors from the MKT-BR group presented with an average length of 10.7 mm, width of 12.0 mm and height of 8.4 mm whereas tumors from the 92.1 group showed an average length of 11.0 mm, width of 11.8 mm and height of 7.4 mm. Ciliary body involvement was found in 20% of the rabbit eyes injected with the MKT-BR cell line and 14% of the rabbit eyes injected with the 92.1 cell line. None of the eyes implanted with MKT-BR cells showed multicentric intraocular melanomas, however 9 of 14 eyes (64.3 %) from the 92.1 injected group showed this multifocal growth pattern. Conclusions: Ultrasound is an excellent method to determine tumor dimension, ciliary body involvement and multicentric tumor growth, in this animal model. The tumors obtained from the two cell lines did not show differences in size or ciliary body involvement. The cell line with high metastatic potential produced tumors with a multicentric growth pattern. Ultrasound should be performed to diagnose and evaluate the tumor progression in uveal melanoma animal models.

Keywords: melanoma • animal model