The present invention relates to a method for treating gefitinib-resistant non-small-cell lung cancer (NSCLC) comprising administering an effective amount of a resveratrol analog, (Z)3,4,5,4′-tetramethoxystilbene (TMS), to a subject in need thereof. The present invention also relates to a method for inducing apoptosis in gefitinib-resistant NSCLC cells comprising contacting the resveratrol analog to the cells at an effective amount. The present methods are mediated by different signaling pathways connected to cell proliferation and differentiation such as mTOR, JNK, and certain EGFR phosphorylated tyrosine kinase.