SLC7A11 and neoplasm: TRX was found to be overexpressed in human melanoma and is positively associated with metastasis [174]; studies using human tumor biopsy samples demonstrated that overexpression of xCT was correlated with melanoma stage and progression, and xenograft studies confirmed the ability of xCT overexpression in melanoma cells to lead to more aggressive tumors compared to vector controls [175], an opposite role from that of a member of the GPX family, GPX3, which has been found to correlate to poor prognosis in melanoma [176].