The acquired resistance mechanisms were reported to be EGFR-dependent drug resistance, which was induced by remutation of the EGFR gene (on-target mutation), EGFR-independent drug resistance induced by other gene mutations (off-target mutation), and pathological transformation, such as transformation into small cell lung cancer (SCLC) and lung squamous cell carcinoma (SqCC). Here, EGFR is linked to small cell lung carcinoma.