This study demonstrates that CAP selectively impairs the ability of hSLC19A1 to transport 5-MTHF while preserving PMX transport, and reduces the uptake of folate by cancer cells without hindering the antifolate therapy, which can help to weaken the antioxidant defense system of cancer cells and elevate intracellular ROS levels, thus enhancing its cytotoxic selectivity toward cancer cells, and prompting cancer cell apoptosis. This evidence concerns the gene SLC19A1 and cancer.