The “more serious” comparison depends on context because the biology differs. Small cell lung cancer (SCLC) is typically more aggressive, grows faster, and spreads earlier, so advanced-stage presentation is common. NSCLC often progresses more slowly and may be curable with surgery when caught early. However, NSCLC becomes highly serious in Stage III–IV as well. Importantly, NSCLC has multiple actionable biomarkers, and targeted therapy or immunotherapy can deliver major benefits in selected patients—sometimes shifting prognosis meaningfully. Therefore, seriousness is best assessed by stage, metastatic sites, overall health, and molecular profile rather than by subtype alone.