Disseminated Melanoma Cells in Bone Marrow From an Immuno–Suppressed Rabbit Model

Abstract

Abstract: : Purpose: Recent studies have shown that the most commonly used method for evaluating metastasis in uveal melanoma, Liver Function Tests (LFTs) are only 14.7% sensitive despite their high specificity. Because uveal melanoma is the most common primary ocular tumour among adults and 50% of patients die within an average of 15 years following the initial diagnosis, it is necessary to develop a precise method of detecting the hematogenous dissemination of this disease. In addition, cutaneous melanoma is among the top ten most common cancers in the United States. Cutaneous melanoma disseminates via lymphatic and hematogenous routes and has a high rate of metastasis in later stages of the disease. This study examines the use of bone marrow biopsies as a method of detecting disseminated cells based on an immuno–suppressed rabbit model of uveal and cutaneous melanoma. Methods: Following a published protocol from our laboratory, thirty albino New Zealand rabbits were immuno–suppressed using cyclosporin A. The rabbits were subsequently injected with 1x106 melanoma cells into their suprachoroidal space. Fifteen of the rabbits were injected with the cutaneous melanoma cell line WM–266–4, while the other 15 were injected with the uveal melanoma cell line 92.1. Two samples of bone marrow were harvested from 29 rabbits upon sacrifice. One of these samples was then cultured in vitro. The second group of samples was subjected to nested RT–PCR using the markers Tyrosinase and Melan–A to determine the presence of disseminated malignant cells. Results: From the cell culture, 2 of the rabbits with cutaneous melanoma and 2 with uveal melanoma exhibited malignant cells similar to those implanted in their eyes. Among the rabbits with cutaneous melanoma, only one was positive for disseminated malignant cells, expressing Melan–A. One rabbit with uveal melanoma expressed Tyrosinase and another one was positive for Melan–A. There was no correlation between the positive specimens for disseminated malignant cells from cell culture and those from PCR among the uveal or cutaneous samples. The rabbits that exhibited disseminated malignant cells in their bone marrow were all sacrificed at different time points in the twelve–week model. Conclusions: This study demonstrates that bone marrow from rabbits with cutaneous and uveal melanoma does contain disseminated malignant cells. Furthermore, it is clear that these disseminated cells are expressed at varying stages in the progression of the disease and that further studies into the sensitivity of bone marrow biopsies are warranted.

Keywords: melanoma • oncology