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Lung adenocarcinoma — overview

TL;DR — Lung adenocarcinoma, the most common lung-cancer histology (Travis 2011, PMID 21252716), became the template for precision oncology: IPASS proved in 2009 that an EGFR mutation — not clinical profile — predicts TKI benefit (PFS HR 0.48 mutation-positive vs 2.85 mutation-negative; Mok 2009, PMID 19692680), and the field has since produced approved targeted therapy for EGFR, ALK, ROS1, KRAS G12C, BRAF V600E, RET, MET exon 14, and HER2 disease, each anchored by its own trial. Tumors without actionable drivers get PD-L1-stratified immunotherapy ± chemotherapy (Reck 2016, PMID 27718847; Gandhi 2018, PMID 29658856). Low-dose CT screening cuts lung-cancer mortality in two RCTs (NLST, PMID 21714641; NELSON, PMID 31995683), and US population mortality from NSCLC has fallen faster than incidence, with survival gains timed to targeted-therapy approvals (Howlader 2020, PMID 32786189). Biggest open front: never-smoker adenocarcinoma (~25% of lung cancer) with its distinct, pollution-linked mutational landscape (Díaz-Gay 2025, PMID 40604281), and how to sequence therapy as targeted agents and immunotherapy move into early-stage disease.

Definition and diagnostic anchors

  • Adenocarcinoma is a glandular-differentiation NSCLC; the 2011 IASLC/ATS/ERS classification abolished "bronchioloalveolar carcinoma," introduced adenocarcinoma in situ (AIS) and minimally invasive adenocarcinoma (MIA) — both with ~100% disease-specific survival after resection — and mandated classifying NSCLC into adenocarcinoma vs squamous whenever possible, because histology directs EGFR testing, pemetrexed use, and bevacizumab safety (Travis 2011, PMID 21252716).
  • Histology-specific chemotherapy is real: pemetrexed is superior in nonsquamous NSCLC across three registration trials with a treatment-by-histology interaction (Scagliotti 2011, PMID 21119545).
  • Molecular testing of every advanced adenocarcinoma is guideline-mandated (CAP/IASLC/AMP: Lindeman 2018, PMID 29398453) — the diagnostic anchor is now genotype, not just morphology.

Headline epidemiology

  • Lung cancer is the top cause of cancer death worldwide (Bray 2024, PMID 38572751); adenocarcinoma is its most common histology (Travis 2011, PMID 21252716; TCGA 2014, PMID 25079552).
  • Stage-shift and screening: NLST showed low-dose CT screening reduces lung-cancer mortality vs chest radiography in high-risk smokers (PMID 21714641); NELSON confirmed mortality reduction with volume-based CT screening in 13,195 men plus a female subgroup (de Koning 2020, PMID 31995683). USPSTF 2021 lowered eligibility to age 50 and 20 pack-years (PMID 33687470).
  • Treatment-driven mortality decline: US incidence-based NSCLC mortality fell 6.3%/yr in men 2013–2016 while incidence fell only 3.1%/yr; 2-yr lung-cancer-specific survival rose from 26% (2001 diagnoses) to 35% (2014) — timed to targeted-therapy approval and absent in small-cell disease (Howlader 2020, PMID 32786189).
  • Never-smokers: lung cancer in never-smokers accounts for up to ~25% of lung cancers, is predominantly adenocarcinoma, and shows geographically patterned mutagenesis (KRAS mutations 3.8× more common in never-smoker adenocarcinomas from North America/Europe; air-pollution-associated signatures) (Díaz-Gay 2025, PMID 40604281).

Molecular landscape (sketch)

TCGA profiling of 230 resected adenocarcinomas found a mean 8.9 somatic mutations/Mb and 18 significantly mutated genes, including activating RIT1 and loss-of-function MGA; recurrent alterations concentrate in RTK/RAS/RAF signaling (TCGA 2014, PMID 25079552). The clinically actionable partition below is a treatment map, not a prevalence table; frequencies vary by smoking history, ancestry, stage, and assay.

Driver Therapy anchor (verified trial) Key result
EGFR (ex19del/L858R) IPASS gefitinib (Mok 2009, PMID 19692680); FLAURA osimertinib (Soria 2018, PMID 29151359) IPASS: PFS HR 0.48 if EGFR-mut; FLAURA: osimertinib > 1st-gen TKI
EGFR, resected stage IB–IIIA ADAURA adjuvant osimertinib (Wu 2020, PMID 32955177) DFS strongly improved (double-blind phase 3)
ALK fusion ALEX alectinib (Peters 2017, PMID 28586279); CROWN lorlatinib (Shaw 2020, PMID 33207094) CNS-active TKIs supersede crizotinib
ROS1 fusion Crizotinib expansion cohort (Shaw 2014, PMID 25264305) ORR 72%, median PFS 19.2 mo
KRAS G12C (~13% of adenoca) CodeBreaK100 sotorasib (Skoulidis 2021, PMID 34096690) First drugging of KRAS; ORR ~37% (phase 2)
BRAF V600E (1–2%) Dabrafenib + trametinib, first line (Planchard 2017, PMID 28919011) Phase 2, practice-adopted
RET fusion (1–2%) Selpercatinib (Drilon 2020, PMID 32846060) High, durable response incl. CNS
MET exon 14 skipping (3–4%) Capmatinib (Wolf 2020, PMID 32877583) GEOMETRY phase 2
HER2 mutation Trastuzumab deruxtecan (Li 2022, PMID 34534430) ORR 55%; ILD risk 26%

Treatment landscape beyond targeted therapy

  • No driver, PD-L1 ≥50%: pembrolizumab monotherapy beat chemotherapy (KEYNOTE-024; Reck 2016, PMID 27718847).
  • No driver, any PD-L1: pembrolizumab + platinum-pemetrexed (KEYNOTE-189; Gandhi 2018, PMID 29658856) is the nonsquamous chemo-IO anchor.
  • Resectable disease: neoadjuvant nivolumab + chemotherapy improved event-free survival and pathologic complete response (CheckMate 816; Forde 2022, PMID 35403841); adjuvant osimertinib for EGFR-mutant resected disease (ADAURA; Wu 2020, PMID 32955177) — adjuvant EGFR-TKI benefit is consistent in network meta-analysis (DFS HR 0.2 for chemo→osimertinib vs chemo; Tian 2022, PMID 35695676).
  • Molecular testing before first-line therapy is the load-bearing step (Lindeman 2018, PMID 29398453); shared immunotherapy, staging, and screening evidence is labeled as NSCLC-wide and cross-linked to the squamous sibling rather than presented as adenocarcinoma-only.

A stage-by-biology map

Anatomy defines whether treatment is curative-intent; biology defines which systemic component belongs in that plan. Neither can substitute for the other.

Clinical state Local-treatment frame Systemic-treatment frame Principal uncertainty
AIS/MIA, completely resected Surgery, often parenchymal-sparing in selected lesions None established Reliable pre/intraoperative recognition
Small peripheral stage I invasive Lobectomy or protocol-selected sublobar resection; SABR if inoperable Biomarker-defined adjuvant treatment only in eligible risk groups Extent of resection, STAS, grade, MRD
Resectable stage II–III Surgery within multidisciplinary sequence Platinum chemotherapy; driver-targeted or perioperative immune pathway Neoadjuvant-only versus perioperative IO; adjuvant duration
Unresectable stage III Definitive concurrent chemoradiation when fit Consolidation selected by genotype and current evidence Driver-specific consolidation and pneumonitis risk
Oligometastatic/oligoprogressive Ablate all sites in selected patients Continue or change systemic suppression Selection after modern CNS-active TKIs
Widespread metastatic Symptom-directed local therapy Exact-driver therapy or PD-L1/fitness-directed chemo-IO Lifetime sequence and resistance

TNM ninth edition changed nodal and metastatic subdivisions but remains an anatomic classification; it does not encode EGFR, ALK, histologic grade, PD-L1, or ctDNA (Rami-Porta 2024, PMID 38447919; Detterbeck 2024, PMID 38885896).

The treatment-selection sequence

  1. Confirm pulmonary adenocarcinoma and exclude a metastasis from another primary.
  2. Record TNM descriptors and edition, sites of disease, symptoms, and brain involvement.
  3. Obtain broad DNA testing with RNA-capable fusion detection and PD-L1 before first systemic therapy when clinically feasible (Lindeman 2018, PMID 29398453).
  4. If an actionable driver exists, follow the exact genotype pathway; do not let high PD-L1 override it.
  5. If driver-negative, select checkpoint monotherapy or chemo-immunotherapy by PD-L1, tempo, burden, fitness, and preference (PMIDs: 27718847, 29658856).
  6. At progression, separate oligoprogression, CNS-only progression, systemic resistance, and histologic transformation before changing therapy.

This order prevents the common category error of treating biomarkers as a flat menu. EGFR exon-19 deletion, EGFR exon-20 insertion, HER2 mutation, HER2 amplification, and PD-L1 expression are different analytes with different evidence.

Recurring evidence boundaries

Claim type What strong evidence looks like Frequent overstatement
Predictive biomarker Treatment-by-marker interaction or genotype-restricted randomized trial Response in a small single-arm cohort
CNS activity Prespecified measurable-CNS denominator and intracranial duration Systemic ORR
Adjuvant cure Mature overall survival and post-relapse treatment accounting Disease-free-survival improvement alone
MRD utility Randomized benefit from acting on ctDNA Prognostic association with recurrence
Screening benefit Mortality reduction in an eligible population High cancer-detection yield
Guideline currency Issuer, version, jurisdiction, access date A paper title without version control
Patient centeredness Longitudinal symptoms, function, time and financial burden Mean adverse-event incidence only

Shared and adenocarcinoma-specific domains

Screening, TNM, surgery, chemoradiation, checkpoint toxicities, brain-metastasis management, and palliative care are largely NSCLC-wide. This condition retains concise evidence because histology and genotype modify how those shared tools are used, while the lung-squamous-cell-carcinoma sibling provides the deliberate contrast.

Adenocarcinoma-specific load-bearing domains are:

  • glandular pattern, AIS/MIA, invasive mucinous disease, grade, and STAS;
  • comprehensive genomic testing and RNA fusion detection;
  • driver-specific first-line and resistance sequences;
  • never-smoker and air-pollution epidemiology;
  • chronic survivorship on oral targeted therapy; and
  • the safety problem of immunotherapy given before a targetable driver is known.

Natural history and evolution

TRACERx demonstrates branched evolution, subclonal selection, and chromosomal instability across primary regions and relapse (Frankell 2023, PMID 37046096). A biopsy is therefore a sample of one place and time, not a complete immutable tumor identity.

Mixed lesion-level response can reflect different resistant subclones; plasma can integrate shedding across sites but misses low-shedding and CNS-confined disease. Tissue remains necessary when small-cell or squamous transformation would change treatment.

Prevention and early detection boundary

Tobacco control remains the largest population lever even in an adenocarcinoma-focused wiki. LDCT reduces mortality in high-risk smoking-exposed populations, while risk-enriched never-smoker CT cohorts currently establish detection yield rather than mortality benefit (NLST/NELSON PMIDs: 21714641, 31995683; TALENT PMID 38042167).

Air pollution is both epidemiologic and mechanistic evidence: particulate exposure associates with adenocarcinoma risk, and experimental work supports IL-1β-mediated promotion of pre-existing EGFR-mutant clones (Hill 2023, PMID 37020004). This does not make individual causation inferable from a tumor genotype.

Frontier map

Frontier Near-term testable question
Never-smoker screening Can a risk model produce favorable deaths-prevented-to-harm balance?
Targeted-therapy intensification Which baseline state needs combination rather than monotherapy?
Resistance Can paired tissue/plasma allocate a rational next inhibitor?
Perioperative treatment Is postoperative checkpoint therapy necessary after neoadjuvant response?
MRD Does acting on ctDNA improve cure or safely reduce therapy?
ADCs Can payload and dose preserve response while reducing ILD?
Spatial biology Can microenvironment states become reproducible clinical assays?
Patient experience How should chronic metastatic TKI survivorship be organized?

Sherlock-Lung links geography and exposure-associated mutational signatures across never-smoker tumors (Díaz-Gay 2025, PMID 40604281). ctDNA/MRD, next-generation inhibitors, bispecific antibodies, and ADCs are active waves, but each needs prospective decision-utility evidence rather than biomarker enthusiasm alone.

Open questions

  • Can screening reach the never-smoker quarter of lung cancer, which falls entirely outside pack-year-based eligibility (USPSTF 2021, PMID 33687470; Díaz-Gay 2025, PMID 40604281)?
  • What is the true population-level contribution of screening vs treatment to the mortality decline (Howlader 2020 attributes the 2013–2016 fall largely to treatment, PMID 32786189; NLST/NELSON prove screening efficacy, PMIDs: 21714641, 31995683)?
  • Does adjuvant osimertinib cure or defer? ADAURA's DFS benefit (Wu 2020, PMID 32955177) leaves the OS-vs-retreatment question central to the adjuvant-TKI debate (Tian 2022, PMID 35695676).
  • Why do KRAS G12C inhibitors underperform EGFR/ALK TKIs (ORR ~37% vs >70%; Skoulidis 2021, PMID 34096690 vs Shaw 2014, PMID 25264305), and what combinations fix this?
  • How should immunotherapy be used in driver-positive disease, where single-agent benefit is limited and TKI-IO sequencing carries toxicity — a gap the testing guideline can name but trials have not resolved (Lindeman 2018, PMID 29398453)?

References

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