To further investigate whether POLA2 could be a potential resistance biomarker in NSCLC, its expression levels were examined in four NSCLC cell lines; PC9 and HCC827, Erlotinib-sensitive cell lines; H1299 and A549, Erlotinib-resistant cell lines, to assess the correlation between Erlotinib and POLA2 levels (Figure 5a). The gene discussed is POLA2; the disease is non-small cell lung carcinoma.