Molecular Pathology of Advanced NSCLC: Biomarkers and Therapeutic Decisions

<b>Background:</b> Advances in molecular pathology have transformed NSCLC (Non-Small Cell Lung Cancer) diagnosis, prognosis, and treatment by enabling precise tumor characterization and targeted therapeutic strategies. We review key genomic alterations in NSCLC, including <i>EGFR</i> (epidermal growth factor receptor) mutations, <i>ALK</i> (anaplastic lymphoma kinase) and <i>ROS1</i> (ROS proto-oncogene 1) rearrangements, <i>BRAF</i> (B-Raf proto-oncogene serine/threonine kinase) mutations, <i>MET</i> (mesenchymal-epithelial transition factor) alterations, <i>KRAS</i> (Kirsten rat sarcoma) mutations, <i>HER2</i> (human epidermal growth factor receptor 2) alterations and emerging <i>NTRK</i> (neurotrophic receptor tyrosine kinase) fusions and <i>AXL</i>-related pathways. <b>Methods:</b> A total of 48 patients with NSCLC was analyzed, including 22 women and 26 men (mean age 70 years, range 44-86). Tumor specimens were classified histologically as adenocarcinomas (<i>n</i> = 81%) or squamous cell carcinomas (<i>n</i> = 19%). Smoking history, PD-L1 (programmed death-ligand 1) expression, and genetic alterations were assessed. NGS (Next-generation sequencing) identified genomic variants, which were classified according to ACMG (American College of Medical Genetics and Genomics) guidelines. <b>Results:</b> The cohort consisted of 29 former smokers, 13 current smokers, and 5 non-smokers (12%), with a mean smoking burden of 33 pack years. PD-L1 TPS (tumor proportion score) was ≥50% in 10 patients, ≥1-<50% in 22, and <1% in 15 patients. In total, 120 genomic variants were detected (allele frequency ≥ 5%). Of these, 52 (43%) were classified as likely pathogenic or pathogenic, 48 (40%) as variants of unknown significance, and 20 (17%) as benign or likely benign. The most frequently altered genes were <i>TP53</i> (tumor protein p53) (31%), <i>KRAS</i> and <i>EGFR</i> (15% each), and <i>STK11</i> (serine/threonine kinase 11) (12%). Adenocarcinomas accounted for 89% of all alterations, with <i>TP53</i> (21%) and <i>KRAS</i> (15%) being most common, while squamous cell carcinomas predominantly harbored <i>TP53</i> (38%) and <i>MET</i> (15%) mutations. In patients with PD-L1 TPS ≥ 50%, <i>KRAS</i> mutations were enriched (50%), particularly <i>KRAS</i> G12C and G12D, with frequent co-occurrence of <i>TP53</i> mutations (20%). No pathogenic EGFR mutations were detected in this subgroup. <b>Conclusions:</b> Comprehensive genomic profiling in NSCLC revealed a high prevalence of clinically relevant mutations, with <i>TP53</i>, <i>KRAS</i> and <i>EGFR</i> as the dominant drivers. The strong association of <i>KRAS</i> mutations with high PD-L1 expression, irrespective of smoking history, highlights the interplay between genetic and immunological pathways in NSCLC. These findings support the routine implementation of broad molecular testing to guide precision oncology approaches in both adenocarcinoma and squamous cell carcinoma patients.