Furthermore, the safety and preliminary anti-tumor activity of the combination therapy in EGFR mutant NSCLC patients who developed acquired resistance (AR) to BIBW 2992, will be assessed in a sequential arm. The sequential arm will use a two-stage design with an early stopping rule after 12 patients with acquired resistance to BIBW 2992 have received up to 5 courses of BIBW 2992 plus cetuximab. If no responses are seen in 12 patients during 5 courses of combination therapy, accrual in the sequential arm will stop. If 1 or more responses are observed, the sequential arm will expand up to about 40 patients.