Assessment of the types and frequency of EGFR and KRAS mutations in NSCLC, as well clinical-prognostic correlations has been extensively studied in many populations. Few Brazilian studies evaluating mutational status in NSCLC has been done so far, none of then explored the regional background nor have considered the quantitative analysis of mutant cell in each sample. Quantitative analysis of the tumor maybe relevant for treatment design for positive samples, p.e a tumor with 90% of mutant clones versus a 15% of mutant clones, which can be obtained currently by the method of pyrosequencing. In this study, we will assess EGFR and KRAS status through the pyrosequencing quantitative technique, and we will also correlate these with clinical-pathological variables among both adenocarcinoma and squamous cell histological subtypes. So far, we have no study that have made this correlation in our review.