Within gastric cancer (GC)—across AGS, MKN-45, SGC-7901, and HGC-27 models—coumarin scaffolds have been investigated as modulators of PI3K/Akt/mTOR and MAPK/ERK signaling, EGFR/HER2 and VEGFR-2–linked angiogenesis, with reproducible caspase-mediated apoptosis and G1/G2–M arrest; MDR/P-gp and context-dependent autophagy also emerge as modifiers of response and exposure. The gene discussed is PGP; the disease is gastric cancer.