Slower growth of ABCB1 overexpressing cancer cells has been reported while this phenomenon could be contributed by multiple factors such as hypoxic conditions of cells or oxygen gradients in spheroids, alteration in expression of fibroblast growth factor and vascular endothelial growth factor, and intercellular transfer of ABCB1 within a heterogeneous tumor.33, 34. This evidence concerns the gene ABCB1 and cancer.