The results of branebrutinib inhibiting P-gp-mediated drug efflux (Figure 2) without altering the protein expression of P-gp (Figure 3) in KB-V-1 and NCI-ADR-RES cancer cells suggest that branebrutinib reverses P-gp-mediated MDR by blocking the drug transport function of P-gp and consequently restores the susceptibility of P-gp-overexpressing multidrug-resistant cancer cells to drug-induced apoptosis (Figure 4). The gene discussed is PGP; the disease is cancer.