After exposure of breast cancer 2D and 3D cultures to complex and free components, only a dose of 0.632 μg/mL SWCNT–COOH–CDDP activated caspase-3 in both 2D and 3D cultures after 24 and 48 h, respectively, demonstrating the activation of the apoptotic cell death pathway. This evidence concerns the gene CASP3 and breast cancer.