To verify whether the toxic effect of treatment with 5-fluorouracil (5FU), a widely used chemotherapeutic in GC, is exacerbated by the inhibition of the TGF-β signaling pathway, we continued the experiments with AGS and SNU-1, the two cell lines resulted more resistant to the toxic effect of SB431542 (the corresponding experiments on KATO III are shown in Figures S2 and S3). The gene discussed is TGFB1; the disease is gastric cancer.