To uncover the undefined effects of metformin on insulin signaling and the difference between cancer cells and non-cancer cells, we selected HEK293T, a human embryonic kidney cell line, and MDA-MB-231, a human breast cancer cell line, to examine the effects of PTP1B S-sulfhydration, redox state, and thiol metabolite contents under insulin and metformin treatment. This evidence concerns the gene PTPN1 and cancer.