NSCLC (Part 1): Biology, Screening, Staging, Early-Stage and Stage III

Overview

• Epidemiology (US, 2026): ~229,410 new cases, ~124,990 deaths (ACS 2026 estimates). Leading cause of ca death in both sexes. 2nd most common ca in men (behind prostate) and women (behind breast).
• 5-yr OS all stages ~28% (was ~17% a decade ago). Stage IV ~10%. Black > White incidence and mortality. Improvement 2/2 ↓ smoking, screening-related stage migration, IO/targeted tx.
• Sex-specific: more women die of lung ca/yr than breast + cervical + uterine combined. Overall, lung ca causes more deaths than colorectal (2nd) + pancreatic (3rd) ca combined (ACS 2026).
• Risk factors:
  • Tobacco: 80 to 90% of all lung ca (~50% of cases in former smokers). Duration > pack count for risk. 10 to 15 yrs cessation halves risk vs continued smoking but stays well above never-smoker risk for decades. E-cigs NOT recommended for cessation (may ↑ likelihood of cigarette smoking).
  • Carcinogens: polycyclic aromatic hydrocarbons and tobacco-specific N-nitrosamines (including nitrosamine ketone NNK and N'-nitrosonornicotine NNN) → P450-activated DNA adducts. Benzo(a)pyrene diol epoxide adducts distribute preferentially along TP53 exons at codons 157, 248, and 273, the same TP53 mutational hot spots.
  • Radon: naturally occurring inert gas, decay product of uranium; 2nd leading cause; 2 to 10% of lung ca. ↑↑ in miners.
  • Other occupational: asbestos, arsenic, nickel, chromium, diesel exhaust, silica.
  • Prior thoracic RT: breast ca, Hodgkin/NHL survivors, ↑↑ if continued smoking.
• Family history / germline:
  • Leukocyte DNA adduct levels associated with lung ca (OR 1.86; in never smokers OR 4.04).
  • Germline EGFR T790M (autosomal dominant): suspect when high-allele-fraction T790M is found pre-TKI; refer for genetic counseling. T790M is most frequently associated with resistance to 1st- and 2nd-gen TKIs.
  • GSTM1/GSTT1, CYP1A1 polymorphisms: modulate carcinogen activation/detox (more relevant in smokers).

Histology

• Historical shift: SCC was the most common lung ca until ~1987, when adenocarcinoma overtook it, largely attributed to introduction of filtered/low-tar cigarettes.
• Adenocarcinoma (~50%, MC subtype): peripheral, arises in scar, often non/light smokers. CK7+, CK20−, TTF-1+ (usually). Highest yield for actionable mutations of any subtype.
  • Mucinous adeno (~5%): tend to be multicentric, TTF-1−, rarely harbor sensitizing EGFR, KRAS-enriched.
  • Nonmucinous adeno (50 to 60%): tend to be solitary, TTF-1+, EGFR-enriched; develops in never smokers more than other subtypes.
  • Adeno precursor sequence: atypical adenomatous hyperplasia (small few-mm bronchoalveolar proliferation of mildly atypical cuboidal/low-columnar cells; unclear prognostic significance) → adenocarcinoma in situ (AIS, ground-glass on CT; pure AIS uncommon; a lepidic lesion with an invasive focus is MIA (invasion ≤5 mm) or invasive adeno, not AIS) → minimally invasive adeno → invasive adeno.
• Squamous cell (~25%): central, cavitates, involves segmental/lobar/mainstem bronchi, heavy smokers. p40/p63+, CK5/6+, intercellular bridging, keratin (squamous) pearls, keratinization.
  • Tx caveats: pemetrexed contraindicated; bevacizumab contraindicated (hemoptysis risk).
• Large-cell carcinoma: diagnosis of exclusion; poorly differentiated large cells with abundant cytoplasm and large nucleoli; treat as adenocarcinoma (nonsquamous NSCLC).
• Large-cell neuroendocrine ca (LCNEC): high-grade NE NSCLC; neuroendocrine morphology (organoid nesting, palisading, trabecular pattern, rosette-like structures); histologically resembles SCLC but larger cells, more cytoplasm, less nuclear molding. Tx as SCLC if pure NE phenotype; strongly smoking-associated.
• Carcinoid (typical, atypical): distinct entity from NSCLC (20 to 40% of carcinoids occur in nonsmokers).
  • Typical: <2 mitoses per 2 mm2, no necrosis. Low-grade, indolent.
  • Atypical: 2 to 10 mitoses and/or focal necrosis. Larger, higher risk of distant mets at presentation, significantly ↓ OS.
  • Markers: chromogranin A+, synaptophysin+, neurosecretory granules on EM.
• SCLC (for contrast): small cells, scant cytoplasm, finely granular chromatin, absent nucleoli, nuclear molding and chromatin smearing (crush artifact); frequent mitoses and extensive necrosis; chromogranin/synaptophysin overexpressed. Almost exclusively heavy smokers, central with bulky lymphadenopathy, paraneoplastic syndromes; rapid growth and clinical course.
• Rare primaries: sarcomas, sarcomatoid/sarcomatous ca (giant cell ca, carcinosarcoma, pulmonary blastoma), salivary-gland-type (mucoepidermoid, adenoid cystic).

Screening

• Low-dose CT (LDCT): noncontrast thin-slice helical/spiral CT of pulmonary parenchyma only (no IV contrast), performed in one breath at low radiation dose.
• USPSTF 2021: annual LDCT in adults 50 to 80 yo with ≥20 pack-yr hx, currently smoke OR quit within 15 yrs. (Updated from 55 to 80 yo / 30 PY in 2013, nearly doubling the eligible population.)
• Stop screening when 15 yrs since cessation OR comorbidities preclude curative tx.
• Evidence:
  • NLST: annual LDCT ×3 yrs vs CXR in older heavy smokers, 20% relative ↓ in lung-ca mortality (P=.004).
  • NELSON: 24% ↓ in men (primary analysis, 10 yrs); 33% ↓ in women (small subgroup, NS).
• Smoking cessation is the single most effective intervention to reduce lung-ca mortality in active smokers.

Clinical presentation & paraneoplastic syndromes

• Metastatic disease at dx common: SCLC (~75%), adenocarcinoma (~50%). MC sites brain (>20%), bone and liver (20 to 30%), adrenal. Always do brain MRI for stage II to IV workup.
• SVC syndrome: SVC obstructed by tumor, thrombus, or nodal mets; oncologic emergency. Distended anterior chest/neck collaterals, facial/neck/arm swelling, headache, cyanosis, Pemberton sign. Tx: stenting, RT, or chemo per histology.
• Hypercalcemia from PTHrP and diffuse skeletal mets, squamous.
• Hypertrophic pulmonary osteoarthropathy (clubbing + painful periostitis of long bones), adenocarcinoma.
• Paraneoplastic neuro (mostly SCLC, but high-yield):
  • SIADH (euvolemic hypoosmolar hyponatremia) and ectopic ACTH (Cushing, often without classic stigmata d/t rapid course; muscle weakness, weight loss, HTN, hyperglycemia, profound hypokalemia).
  • LEMS: anti-VGCC (P/Q-type).
  • Cerebellar degeneration: anti-Hu, anti-CV2, anti-ANNA, anti-PCA-2 (note: anti-Yo is PCA-1, typically gyn/breast ca, not lung).
  • Opsoclonus-myoclonus: anti-Ri.
  • Retinal blindness/retinopathy: anti-recoverin.
  • Stiff-person: anti-amphiphysin.
  • Limbic encephalitis: anti-Hu, anti-CRMP5.
  • Sensory neuronopathy: anti-Hu, subacute distal sensory loss with absent DTRs and preserved strength.

Staging, TNM 9th edition (effective Jan 2025)

• Key 9th-ed changes from 8th:
• N2 split: N2a = single station, N2b = multiple stations.
• M1c split: M1c1 = multiple mets in single extrathoracic organ system; M1c2 = multiple organ systems.
• T descriptors: unchanged from 8th ed.
• M descriptors quick reference:
  • M1a: malignant pleural/pericardial effusion, separate tumor nodule in contralateral lung, or pleural/pericardial nodules.
  • M1b: single extrathoracic met.
  • M1c1/c2: multiple extrathoracic mets (single vs multiple organ systems).

• Station 1 (low cervical, supraclavicular, sternal notch): midline of trachea divides 1R/1L; N3 if supraclavicular/scalene.
• Stations 2 to 4 (upper and lower paratracheal): superior mediastinal. 2R/2L upper paratracheal; 4R lower paratracheal (to lower border of azygos vein), 4L lower paratracheal (aortic arch to left main PA).
• Station 3: 3A prevascular (anterior to vessels), 3P retrotracheal (posterior to trachea).
• Aortic stations 5 (subaortic, AP window) and 6 (paraaortic): drain L upper lobe; not reachable by mediastinoscopy, need Chamberlain procedure (anterior mediastinotomy).
• Stations 7 (subcarinal), 8 (paraesophageal), 9 (pulmonary ligament): inferior mediastinal.
• Stations 10 to 14 (hilar through subsegmental): N1.

• PET-CT: recommended for all stages considered for curative-intent tx (incl. stage I). Limits: cost/availability, granulomatous/inflammatory false-positives, has reduced sensitivity (false negatives) for lesions <8 to 10 mm, and NEVER a substitute for brain MRI. Preoperative PET reduces futile thoracotomies and detects distant mets. Does not replace invasive mediastinal staging in potentially resectable disease.
• Brain MRI for stage II to IV (consider in stage IB) before curative-intent tx.
• EBUS/EUS: first-line invasive mediastinal staging (samples 2R/2L, 4R/4L, 7, 10, 11); has reduced number of invasive procedures.
• Mediastinoscopy: higher NPV, but cannot reach stations 5/6.

Genomic profiling

• Test all advanced non-squamous NSCLC (NCCN also considers squamous, especially non/light smokers). Broad NGS preferred. PD-L1 by IHC.
• Required actionable targets:
  • Mutations: EGFR (incl. exon 20 ins), KRAS G12C, BRAF V600E, MET exon 14 skipping, HER2 (ERBB2), EGFR T790M (resistance).
  • Fusions/translocations: ALK, ROS1, RET, NTRK1/2/3, NRG1.
  • Copy number: MET (≥10 DNA copies = high).
  • Liquid biopsy (ctDNA): useful when tissue inadequate or to monitor resistance. Negative liquid does NOT rule out, confirm with tissue.
  • Critical: biomarker results MUST be available before starting 1L tx in advanced disease. IO/chemoIO before ruling out drivers worsens outcomes (esp. EGFR/ALK+).

Stage I to II, early-stage

• Lobectomy + mediastinal LN sampling/dissection, standard of care (5-yr OS ~50% in stage I to II). In peripheral ≤2 cm node-negative NSCLC, protocol-quality sublobar resection (including wedge) is noninferior for DFS and OS (CALGB 140503); higher local recurrence applies mainly to larger or inadequately staged tumors. Prefer lung-sparing R0 resection: mainstem involvement may allow sleeve lobectomy, trans-fissural extension bilobectomy or en bloc resection; pneumonectomy only if R0 not otherwise achievable.
• Nodal assessment: ≥3 mediastinal stations (incl. station 7) + ≥1 hilar/intrapulmonary (10 to 14), lobe-specific.
• Sublobar resection (segmentectomy or wedge), non-inferior for peripheral cT1aN0 ≤2 cm:
• CALGB 140503 (NEJM 2023): sublobar non-inferior to lobectomy for DFS/OS in cT1aN0 ≤2 cm peripheral NSCLC.
• JCOG0802: segmentectomy showed superior OS vs lobectomy (5-yr 94.3% vs 91.1%) in cIA NSCLC ≤2 cm with C/T ratio >0.5; locoregional recurrence higher.
• En bloc resection of involved ribs + lung: for peripheral chest-wall invasion (T3N0, stage IIB).
• Preoperative pulmonary assessment: predicted postop FEV1 and DLCO. ≤30% predicted = high surgical risk; poor exercise tolerance and need for supplemental O2 also flag high risk.
• VATS preferred over thoracotomy (less morbidity, esp. in pts with ↓ pulmonary reserve).

• Conventional fractionated RT (e.g., 60 Gy in 30 fr of 2 Gy) if surgery contraindicated but good pulmonary reserve: cure in ~20%.
• SBRT for medically inoperable stage I (or pt refusing surgery): delivers less RT to normal parenchyma. 2-yr local recurrence ~4.9%, 5-yr ~10.5%; 5-yr OS ~40%. In operable T1-T2 N0M0, single-arm phase II 4-yr local control 96%. SBRT > standard RT for inoperable stage I (↓ tx failure, HR 0.32). Randomized surgery-vs-RT trials ongoing.
• For central tumors (<2 cm from proximal bronchial tree) use risk-adapted SBRT (e.g., 5 fractions, RTOG 0813) rather than avoidance; ultracentral tumors need extra caution/more fractions; selected >5 cm tumors can be treated after individual assessment (↑ hemoptysis, fistula, bronchial stenosis).
• Role of chemo after RT alone is unclear. Thermal ablation (RFA/microwave) is an option for selected inoperable small peripheral stage I tumors (weaker evidence than surgery/SBRT).

• Definition: apical tumor invading thoracic-inlet structures (chest wall at/above 1st rib, brachial plexus, subclavian vessels); any N. T3 to T4 N0 to N1 are trimodality candidates.
• Clinical clues: Horner syndrome (ptosis, miosis, anhidrosis); shoulder/arm pain in ulnar distribution (rib destruction, C8/T1 nerve root involvement).
• Tx (SWOG 9416 paradigm, PMID 17235046): trimodality, neoadjuvant concurrent chemoRT (cisplatin/etoposide + 45 Gy) → surgery → 2 cycles adjuvant/consolidation chemo. pCR or minimal microscopic disease 56%; 5-yr OS 44% all pts, 54% with complete resection.

Adjuvant therapy after resection

• LACE meta-analysis (PMID 18506026): 5-yr OS benefit ~5% (HR 0.89) for cisplatin doublet in stage II to IIIA (stage II and IIIA each HR 0.83). NO benefit and possible harm in stage IA (HR 1.40). Stage IB HR 0.93 (NS).
• CALGB 9633 (PMID 18809614): resected stage IB, chemo vs obs, overall negative; but tumors ≥4 cm derived OS benefit (HR 0.69).
• Stage IB (T2a, >3 to 4 cm): consider only if high-risk features (high grade, LVI, visceral pleural invasion). "IB ≥4 cm" in CALGB 9633 and adjuvant/neoadjuvant trials is AJCC 7th ed (now T2b, IIA).
• Standard regimens:
  • Cisplatin/vinorelbine, cisplatin/docetaxel, cisplatin/gemcitabine, historical standards (squamous).
  • Cisplatin/pemetrexed, non-squamous (TREAT trial: similar OS, better tolerated than cis/vinorelbine).
  • Carboplatin substitutable in older pts or when cisplatin not tolerated; older pts should not be excluded (LACE efficacy similar despite fewer doses). Start chemo within 8 wks of surgery.

• IMpower010 (PMID 34555333): atezolizumab × 1 yr after adj chemo in resected stage II to IIIA, PD-L1 ≥1%.
  • PD-L1 ≥50% subgroup: DFS HR ~0.43; OS HR 0.47 (exploratory, 5-yr update, JCO 2025); ITT OS not improved (HR 0.97).
  • FDA-approved for resected stage II to IIIA, PD-L1 ≥1% (label does not require EGFR/ALK wild-type; guidelines favor TKI if driver+).
• PEARLS / KEYNOTE-091: pembrolizumab × 1 yr after adj chemo in stage IB (≥4 cm) to IIIA. DFS HR 0.76 in ITT. FDA-approved regardless of PD-L1.

• ADAURA (PMID 32955177): osimertinib × 3 yrs in resected stage IB to IIIA EGFR-mutant (ex19del/L858R). Adj chemo not mandated but similar between arms.
  • Efficacy: 2-yr DFS 89% vs 52%, DFS HR 0.20 (overall IB to IIIA; II to IIIA primary analysis 90% vs 44%, HR 0.17); OS HR 0.49 (2023 update, significant); ↓ CNS relapse.
  • Standard of care; consider after adj chemo.
• ALINA (NEJM 2024): adjuvant alectinib × 2 yrs in resected stage IB (≥4 cm) to IIIA ALK+ NSCLC.
  • Efficacy: DFS HR 0.24 (76% ↓ recurrence/death); CNS DFS HR 0.22.
  • FDA approval: Apr 2024.
• Older adj TKI trials (DFS but not OS benefit): RADIANT (PMID 26324372, erlotinib ×2 yr, EGFR+ DFS trend NS); CTONG1104 (PMID 33332190, gefitinib ×2 yr vs cis/vinorelbine, DFS improved but OS same HR 0.92, likely from crossover TKI use).
• Important: do NOT give adj IO if EGFR/ALK+, start TKI.

Neoadjuvant & perioperative therapy

• Indication: resectable stage II to IIIA (and some IIIB), particularly single-station mediastinal N2, superior sulcus tumors, chest-wall invasion with N1, or node+ disease/comorbidity optimization. Meta-analysis (PMID 24576776) shows ~5% 5-yr OS gain with neoadj chemo (HR 0.87), similar to adj. Neoadj and adj outcomes are similar; pts who receive neoadj chemo generally do not also receive adj chemo.

• CheckMate 816 (PMID 35403841, NEJM 2022): neoadj nivo + chemo × 3 vs chemo × 3 in resectable IB (≥4) to IIIA.
  • Efficacy: pCR 24% vs 2%; EFS HR 0.63; OS HR 0.72; 5-yr OS 65.4% vs 55.0% (final analysis, Forde NEJM 2025).
  • FDA approval: Mar 2022.
• Earlier neoadj IO signals: NEOSTAR (PMID 33603241; nivo vs nivo/ipi; MPR and pCR higher with nivo/ipi, pCR 38% in resected); LCMC3 (neoadj atezolizumab, MPR 20%, pCR 7%, 31% downstaged); NADIM (PMID 32979984; neoadj carbo/paclitaxel + nivo, MPR 83%, pCR 63%).

• KEYNOTE-671: perioperative pembrolizumab + chemo × 4 → surgery → pembro × 13 cycles.
  • Efficacy: EFS HR 0.58; first perioperative IO trial with confirmed OS benefit (HR ~0.72).
  • FDA approval: Oct 2023.
• AEGEAN: perioperative durvalumab + chemo → surgery → durva × 12.
  • Efficacy: EFS HR 0.68; pCR 17% vs 4%.
  • FDA approval: Aug 2024.
• CheckMate 77T: perioperative nivolumab + chemo → surgery → nivo × 1 yr.
  • Efficacy: EFS HR 0.58; pCR 25% vs 5%; OS trend favorable (ASCO 2025 update).
  • FDA approval: Oct 2024.
• NEOTORCH: perioperative toripalimab + chemo (Asia-based; not FDA-approved).
• Practical points:
  • Do NOT use IO if EGFR/ALK+, use TKI.
  • Choice between CheckMate 816 (no adj IO) vs perioperative regimens is debated; perioperative likely favored for higher-stage/PD-L1+ disease.
  • Post-pCR adj IO benefit is questioned, but current label requires completion of the adjuvant phase regardless of pCR.

• NeoADAURA (He J et al, JCO 2025; ASCO 2025 plenary): phase 3, 3-arm, resectable stage II to IIIB N2 EGFR-mut NSCLC, neoadj osimertinib + platinum-chemo × 3 cycles vs neoadj osimertinib mono × ~9 wk vs neoadj chemo × 3 (control), all followed by surgery; adjuvant osimertinib offered to eligible patients post-op (not mandatory for all) per ADAURA.
  • Efficacy: MPR 26% (osi+chemo) vs 25% (osi mono) vs 2% (chemo); pCR 4% vs 9% vs 0%. Both osi arms significantly superior to chemo.
  • Implication: establishes neoadjuvant osimertinib (mono or with chemo) as an option in resectable EGFR+ NSCLC. Do NOT use perioperative IO in EGFR+ disease.

Stage III

• Multimodality required. Options:
• Neoadjuvant chemoIO → surgery (preferred per CheckMate 816 / perioperative trials).
• Neoadjuvant chemoRT → surgery.
• Definitive concurrent chemoRT → consolidation durvalumab (PACIFIC).
• INT 0139 (PMID 19632716): stage T1-3 N2M0, definitive chemoRT (cis/etoposide) +/- surgery. PFS longer with surgery (12.8 vs 10.5 mo) but OS same (23.6 vs 22.2 mo); excess deaths in pts requiring pneumonectomy; lobectomy subgroup favored (post hoc).
• Pearl: avoid pneumonectomy after induction chemoRT.
• Lung-ART: postop RT (PORT) in completely resected pN2 (after adj chemo), no PFS/OS benefit (3-yr OS 66.5% vs 68.5%); no longer SOC.

• Concurrent chemoRT > sequential (↑ OS, ↑ esophagitis) > RT alone.
• Standard regimens:
  • Cisplatin/etoposide × 2 (full dose) with RT 60 Gy; 5-yr OS ~15% (phase II); AEs myelosuppression, RT esophagitis (grade 3-4 ~20%). Consolidation docetaxel is NOT recommended (↑ febrile neutropenia, pneumonitis, hospitalization).
  • Weekly carboplatin/paclitaxel (low weekly doses): more grade ≥2 pneumonitis (33.3% vs 18.9%) but less grade ≥3 esophagitis (6.3% vs 20%) vs cis/etoposide; 3-yr OS favored cis/etoposide (+15%, P=.024), median OS 20.7 vs 23.3 mo (NS) (PMID 28137739).
  • PROCLAIM (PMID 26811519): in non-squamous, cis/pemetrexed vs cis/etoposide with RT, same OS but cis/pemetrexed had fewer grade 3-4 AEs (64% vs 76.8%), including less neutropenia.
  • RT dose: 60 Gy > 74 Gy. RTOG 0617, 74 Gy had WORSE OS (not explained by toxicity alone; possibly cardiac dose).
  • PACIFIC (PMID 30280658, OS PMID 33476803): durvalumab × 1 yr after concurrent chemoRT (54 to 66 Gy, ≥2 cycles chemo) in unresectable stage III without progression.
    • Efficacy: PFS 17.2 vs 5.6 mo (HR 0.55); OS HR 0.72; 5-yr OS 43% vs 33%; ↓ new lesions/brain mets (6.3% vs 11.8%).
    • Timing: start within 42 days of RT. Grade 3-4 AEs 30.5% vs 26.1%, similar pneumonitis rates.
  • LAURA (NEJM 2024): osimertinib after definitive chemoRT in unresectable stage III EGFR-mutant NSCLC.
    • Efficacy: PFS 39.1 vs 5.6 mo (HR 0.16). New SOC for EGFR exon 19 del or L858R unresectable stage III after chemoRT (LAURA/FDA); other EGFR variants not covered.
    • Replaces durvalumab in EGFR+ subgroup.
  • PACIFIC-2 (negative): adding durvalumab CONCURRENT with chemoRT, no benefit, more toxicity. Stick with sequential per PACIFIC.

Continued in: NSCLC (Part 2): Stage IV, Targeted and Systemic Therapy