# Immunohistochemical Expression of ABCB5 as a Potential Prognostic Factor in Uveal Melanoma
## 4 Discussion  
UM is a rare neoplasm with an \"indolent\" but slowly progressive biological behavior, characterized by the onset of liver metastasis within 10-15 years after diagnosis in about 50% of patients and a high rate of mortality [8]. Although in the last years several improvements have been recorded in the conservative management of UM with the aim of preserving the visual function [20], recurrence of disease and metastasis are still frequent events in the natural history of this neoplasm. Therefore, the study of molecular alterations in UM is currently of great scientific interest aiming at identifying possible biological factors capable of predicting a more aggressive biological behavior of the disease. \begin{table}
\begin{tabular}{c c c} \hline  & **Metastasis (n=23)** & **Metastasis free (n=32)** \\ \hline Low & 10 (43.5\%) * & 18 (56.3\%) \\ High & 13 (56.5\%) & 14 (43.8\%) \\ \hline \end{tabular} Abbreviations: ABCB5, ATP-binding cassette sub-family B member 5. p ([PERSON]’s exact test). * \(p\) = 0.026  
\end{table} 
Table 4: Number of uveal melanoma (with and without metastasis) with low and high ABCB5. Figure 4: Kaplan–Meier survival analyses in patients with uveal melanomas with low and high ABCB5 expression. The log-rank test showed a significant difference (\(p\) = 0.039) between the two groups in ABCB5 expression. Histopathological factor of poor prognosis such as epithelioid cell type, tumor size, mitotic index, tumor infiltrating lymphocytes (TILs), extrascleral invasion, vascular pattern and necrosis, and clinical risk factor (male sex and older age of the patient) are not very accurate in identifying a high-risk prognostic category of patients. Cytogenetic studies demonstrated that patients with disomy 3 have a lower risk of developing metastasis; instead, the loss of heterozygosityosis of chromosome 3 was associated with a high rate of metastatic disease and poorer prognosis in UM: in particular, [PERSON] et al. [21] evaluated 30 patients with UM in association with monosomy 3 and 24 patients with disomy 3, and reported that 50% of patients with monosomy 3 showed metastasis within 3 years, whereas no metastatic disease was noted in those with disomy 3. In recent years, inactivating mutations of BRCA1 associated protein-1 (BAP-1), confirmed by lower nuclear immunohistochemical expression, have been found and reported in literature as poor prognostic factors [22; 23]; moreover, high levels of expression of nestin, a member of the intermediate filament protein family, seem to correlate with metastatic progression and reduced survival rate in UM [24]. We previously evaluated the expression of ADAM10, RKIP and pRKIP [19; 25], demonstrating their role as negative prognostic markers: in particular, regarding ADAM10 expression, high levels were found in 11/13 patients with metastatic UM and in only 15/39 patients without metastasis, and the difference was statistically significative [19]. As previously said, ABCB5 is a marker of cancer stem cells and is implicated in the tumorigenesis and tumor growth of several neoplasms, such as cutaneous melanoma, breast cancer and hepatocellular carcinoma [9; 10; 11; 12; 13; 14; 15; 16]. Particularly, [PERSON] et al. [17] found that in vitro ABCB5-negative melanoma cell sub-population displayed a reduction in cell migration and invasion compared to the ABCB5-positive one; this finding was also confirmed at the transwell assays: lentivirusus-mediated knockdown of ABCB5 in two different melanoma cell cultures induced a decline of cell migration and invasion. NF-kB signaling pathway has been discovered to be involved in this process: ABCB5 activates the NF-kB pathway by inhibiting p65 ubiquitination to enhance p65 protein stability, resulting in an accumulation of p65 in ABCB5-positive MMICs [17]. Among the traditional NF-kB targeting genes, MMP9 is involved in tumor cells invasion and metastasis [26]: an overexpression of MMP9, induced by ABCB5, seems to be one of the most important steps in the stimulation of metastatic potential of cutaneous melanoma [17].