Cyclin D1 has been identified as a key downstream effector of EGFR signalling by using microarray transcriptional profiling of gefitinib-resistant NSCLC EGFR L858R-T790M mutant H1975 cells exposed to the irreversible and in these cells still effective inhibitor, CL-387,785 versus gefitinib. The gene discussed is EGFR; the disease is non-small cell lung carcinoma.