To begin with, we followed changes in HER3 abundance in erlotinib-resistant PC9ER lung cancer cells (delE746–A750 plus T790M) pre-exposed to combinations of osimertinib, cetuximab, trastuzumab, and mAb33, a neutralizing anti-HER3 mAb we previously generated [32]. This evidence concerns the gene ERBB3 and lung cancer.