Gefitinib (0.01-0.1 mM) results in increased phosphotyrosine load of the receptor, increased signalling to ERK and stimulation of proliferation and anchorage-independent growth, presumably by inducing EGFRvIII dimerisation in long-term exposure of EGFRvIII-expressing cells. On the other hand, gefitinib (1-2 mM) significantly decreases EGFRvIII phosphotyrosine load, EGFRvIII-mediated proliferation and anchorage-independent growth. Gefitinib (ZD1839) inhibits the monolayer growth of these EGF-driven untransformed cells with IC ₅₀ of 20 nM. Gefitinib leads to an inhibition of CALU-3 and GLC82 cell proliferation, with an IC ₅₀ of 2 μM.

Gefitinib (150 mg/kg, p.o.) in conbination with Metformin induces a significant reduction in tumor growth in nude mice bearing H1299 or CALU-3 GEF-R cells that are grown subcutaneously as tumor xenografts. In irradiated rats, Gefitinib treatment augmentes lung inflammation, including inflammatory cell infiltration and pro-inflammatory cytokine expression, while Gefitinib treatment attenuates fibrotic lung remodeling due to the inhibition of lung fibroblast proliferation.