DHFR and breast cancer: Among these drugs are Palbociclib (a cyclin-dependent kinase inhibitor for breast cancer), Dilmapimod (showing potential activity against rheumatoid arthritis), Vistusertib (the novel mTOR inhibitor with kinase activity), Trametinib (a dual-specificity mitogen-activated protein kinase inhibitor), Voxtalisib (a PI3K/mTOR inhibitor with kinase activity), and Piritrexim (a DHFR dihydrofolate reductase inhibitor) [23], as illustrated in Figure 1.