4.6. Cell Viability Assay

SKBR3 and BT474 cells were seeded in a 6-well (2 × 10⁵ cells/well) plate with 2 mL of growth medium and treated with lapatinib the next day. After incubation for 48 and 72 h, cells were incubated with 100 μL of MTT solution for 4 h at 37 °C. The supernatant was removed, and insoluble formazan dye was solved by 100 μL DMSO. Absorbance was measured at 540 nm by a microplate reader.