Lung cancer (LC) is the tumor responsible for the highest mortality worldwide. Lung adenocarcinoma is the major subtype of lung cancer and represents the deadliest human cancer, affecting current-, ex-, and even non-smokers. Osimertinib is indicated as monotherapy for the first-line (1L) treatment of adult patients with locally advanced or metastatic NSCLC with activating mutations in the EGFR, for the treatment of adult patients with EGFR T790M mutation-positive locally advanced or metastatic NSCLC, for the adjuvant treatment of adult patients with NSCLC stages IB-IIIA after complete resection of the tumor that has activating mutations of the EGFR, for the treatment of adult patients with locally advanced, unresectable NSCLC whose tumours have EGFR exon 19 deletions or exon 21 substitution mutation and whose disease has not progressed during or following platinum-based chemoradiation therapy, and in combination with pemetrexed and platinum-based chemotherapy for the 1L treatment of adult patients with advanced NSCLC whose tumours have EGFR exon 19 deletions or exon 21 substitution mutations. The FLAURA trial showed that treatment with osimertinib significantly prolongs PFS and improves overall survival (OS) compared to standard EGFR tyrosine kinase inhibitors. The results of the ADAURA study showed a reduction in the risk of recurrence or death by 83% in stages II to IIIA, and in 80% in stages IB-IIIA. Additionally, osimertinib demonstrated a highly statistically significant improvement in DFS and HRQoL was maintained. The FLAURA2 trial showed that 1L treatment with osimertinib-chemotherapy led to significantly longer progression-free survival than osimertinib monotherapy among patients with EGFR mutated (EGFRm) advanced NSCLC. The LAURA trial showed that treatment with osimertinib after chemoradiotherapy resulted in significantly longer PFS than placebo among patients with unresectable stage III EGFRm NSCLC. To date, there are no real-world data on osimertinib either in 1L treatment in locally advanced or metastatic EGFRm NSCLC nor as adjuvant treatment, in early stages of cancer, regarding effectiveness, adherence, treatment exposure and quality of life (QoL), among others, and in particular for the use of osimertinib in subpopulations less represented in pivotal trials such as elderly or patients with uncommon EGFR mutations. Furthermore, the duration of treatment in real life in Spain is also a gap, as it appears to be longer than in clinical trials, which means that there are patients who are treated beyond progression. Therefore, this observational ambispective study based on real-world data aims to provide data on osimertinib use as adjuvant treatment in adult patients diagnosed with stages IB-IIIA EGFRm NSCLC, in 1L treatment in patients with locally advanced or metastatic EGFRm NSCLC, as consolidation treatment in patients with locally advanced, unresectable NSCLC whose tumours have EGFR exon 19 deletions or exon 21 substitution mutations and whose disease has not progressed during or following platinum-based chemoradiation therapy, and in combination with pemetrexed and platinum-based chemotherapy in patients with advanced NSCLC whose tumours have EGFR exon 19 deletions or exon 21 (L858R) substitution. Specifically, the study will focus on patient characteristics, adherence, treatment exposure, administration, survival, quality of life, effectiveness and safety providing insights into osimertinib use in daily practice for patients with EGFRm NSCLC, where there are current evidence gaps.