Lung adenocarcinoma: from molecular basis to genome-guided therapy and immunotherapy

Although adenocarcinoma (ADC) is the most frequent lung cancer, its diagnosis is often late, when the local invasion is important and/or the metastases have already appeared. Therefore, the mortality at 5 years is still very high, ranging from 51% to 99%, depending on the stage. The implementation of different molecular techniques has allowed genomic studies even in relatively small histological samples such as obtained with non-invasive or minimally invasive techniques, facilitating a better phenotyping of lung ADC. Thus, current classification differentiates between preinvasive lesions (atypical adenomatous hyperplasia and in situ ADC), minimally invasive ADC (MIA) and invasive ADC. 'Field cancerization' is a concept that refers to progressive loco-regional changes occurring in tissues exposed to carcinogens, due to the interaction of the latter with a predisposing genetic background and an appropriate tissue microenvironment. Somatic genetic alterations, including mutations but also other changes, are necessary for oncogenesis, being especially frequent in lung ADC. Changes in the epidermal growth factor receptor (EGFR) gene, Kirsten rat sarcoma viral oncogene (KRAS), v-Raf murine sarcoma viral oncogene homolog B (BRAF), gene encoding neurofibromin (NF1), anaplastic lymphoma kinase (ALK) and ROS1 are the main genes that suffer alterations in the tumors of patients with ADC. Molecular profiling of these tumors allows more targeted treatments through two distinct strategies, genome-guided therapy and immunotherapy. The former, targets the aberrant pathways secondary to the genomic alteration, whereas the latter may be based on the administration of antibodies [such as those against cytotoxic T-lymphocyte antigen 4 (CTLA-4) or the programmed cell death ligand 1/protein 1 pathway (PD-L1/PD-1)] or the stimulation of the patient's own immune system to produce a specific response. These strategies are obtaining better results in selected ADC patients.