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Lung adenocarcinoma — KRAS, BRAF, MET, and HER2 disease

TL;DR — KRAS, BRAF, MET, and ERBB2/HER2 alterations are not interchangeable “other drivers”: each requires allele- and mechanism-specific interpretation. KRAS G12C inhibitors provide meaningful second-line activity but less depth and durability than many kinase-fusion or EGFR paradigms; randomized sotorasib improved progression-free survival over docetaxel without a demonstrated overall-survival advantage (Skoulidis 2021, PMID 34096690; de Langen 2023, PMID 36764316). BRAF V600E is treated by combined BRAF–MEK inhibition, MET exon-14 skipping by selective MET inhibitors, and HER2-mutant disease by antibody–drug conjugates or emerging HER2-selective TKIs (Planchard 2017, PMID 28919011; Wolf 2020, PMID 32877583; Paik 2020, PMID 32469185; Li 2022, PMID 34534430; Heymach 2025, PMID 40293180). Co-mutations and resistance biology are especially important in KRAS disease. Testing reports must distinguish mutation, amplification, overexpression, and exon-skipping because they do not confer the same therapy sensitivity.

The alteration is the biomarker

Gene Actionable state State that must not be silently substituted Evidence anchor
KRAS G12C substitution “KRAS mutation” broadly; non-G12C alleles CodeBreaK 100/200; KRYSTAL-1 (PMIDs: 34096690, 36764316, 35658005)
BRAF V600E substitution Non-V600 BRAF mutation or amplification Dabrafenib–trametinib and PHAROS (PMIDs: 28919011, 37270692)
MET Exon-14 skipping alteration Low-level amplification or IHC overexpression GEOMETRY mono-1 and VISION (PMIDs: 32877583, 32469185)
HER2/ERBB2 Activating mutation, usually kinase-domain insertion HER2 IHC positivity or amplification without mutation DESTINY-Lung01/02 and zongertinib (PMIDs: 34534430, 37694347, 40293180)

The report should name the exact variant, assay, specimen, tumor fraction, and whether the finding is somatic, germline-suspected, clonal, or subclonal. Broad NGS is preferable to a serial single-gene cascade because these alterations compete for limited tissue and some require copy-number or splice-aware interpretation (Lindeman 2018, PMID 29398453; Yu 2019, PMID 30243889).

KRAS-mutant adenocarcinoma

KRAS is a common lung-adenocarcinoma driver, particularly in tobacco-exposed populations, but its allele distribution varies with exposure and geography (TCGA 2014, PMID 25079552; Díaz-Gay 2025, PMID 40604281). G12C is only one allele; G12D, G12V, G13, Q61, and others require different developmental strategies.

G12C inhibitor evidence

Trial Population Comparison Main result Interpretation
CodeBreaK 100 Previously treated KRAS G12C NSCLC Sotorasib single arm ORR 37.1%; median PFS 6.8 mo Proof of druggability, not comparative benefit (PMID 34096690)
CodeBreaK 200 Previously treated KRAS G12C NSCLC Sotorasib vs docetaxel PFS HR 0.66; median 5.6 vs 4.5 mo Positive PFS; crossover and design complicate OS (PMID 36764316)
KRYSTAL-1 Previously treated KRAS G12C NSCLC Adagrasib single arm ORR 42.9%; median PFS 6.5 mo Intracranial activity reported; no randomized comparator (PMID 35658005)
KRYSTAL-12 Previously treated KRAS G12C NSCLC Adagrasib vs docetaxel Randomized PFS benefit Current comparative anchor for adagrasib (PMID 40783289)

The modest median PFS compared with EGFR-, ALK-, or RET-directed first-line therapy reflects biology and line of therapy, not proof that RAS cannot be targeted. Adaptive feedback reactivates MAPK signaling; parallel PI3K, receptor-tyrosine-kinase, and cell-state programs create heterogeneous escape.

Co-mutations are not footnotes

STK11/LKB1 loss defines an immune-cold subset and was associated with primary resistance to PD-1 blockade in KRAS-mutant lung adenocarcinoma (Skoulidis 2018, PMID 29773717). KEAP1 alterations define a redox-adapted state associated with poor outcomes and diminished immunotherapy sensitivity, although prognostic and predictive effects are difficult to separate (Ricciuti 2022, PMID 34740862; Marinelli 2020, PMID 32866624). Randomized POSEIDON subgroup and translational analyses support CTLA-4-containing chemo-immunotherapy as a resistance-mitigating strategy, but a dedicated prospective biomarker-selection trial is still required (Skoulidis 2024, PMID 39385035).

Co-alteration Typical phenotype Clinical status
TP53 More inflamed phenotype on average; genomic instability Retrospective stratifier, not a standalone therapy selector
STK11 Low T-cell infiltration; metabolic adaptation Adverse marker; prospective regimen selection unproven
KEAP1/NFE2L2 Oxidative-stress program and immune exclusion Adverse marker across therapies; targeted strategies investigational
CDKN2A/B Cell-cycle dysregulation No validated targeted standard

Acquired resistance to G12C inhibitors can involve secondary KRAS mutations, KRAS amplification, NRAS/BRAF/MAP2K1 alterations, MET amplification, fusions, and histologic transformation (Awad 2021, PMID 34161704). A single post-progression plasma sample may underrepresent spatially heterogeneous mechanisms.

BRAF-mutant disease

BRAF V600E activates MAPK signaling as a class-I monomeric mutation and is biologically distinct from non-V600 class-II/III alterations. Dabrafenib plus trametinib produced high response rates in previously untreated V600E-mutant metastatic NSCLC and established combined pathway inhibition (Planchard 2017, PMID 28919011).

PHAROS evaluated encorafenib plus binimetinib and provided another BRAF–MEK doublet option, with separate treatment-naive and previously treated cohorts (Riely 2023, PMID 37270692).

BRAF category Mechanism Evidence implication
V600E High-activity monomer BRAF plus MEK inhibition supported
Class II non-V600 Activating dimer V600-selective inhibitor alone may be inadequate
Class III Kinase-impaired, RAS-dependent Biology and co-drivers dominate; trial strategy preferred
Acquired BRAF after EGFR TKI Bypass resistance Combination must account for persistent EGFR dependence

MET exon-14 skipping disease

MET exon-14 skipping removes the juxtamembrane CBL-binding region, impairs receptor degradation, and increases MET signaling. It often arises in older patients and can coexist with high-level MET amplification, but the splice event—not age or IHC—is the validated selector.

Capmatinib in GEOMETRY mono-1 and tepotinib in VISION produced responses in METex14 NSCLC, with higher response rates in treatment-naive than previously treated cohorts (Wolf 2020, PMID 32877583; Paik 2020, PMID 32469185).

Issue Clinical consequence
Diverse splice-site variants DNA pipelines need validated exon-14 rules; RNA can resolve transcript consequence
Edema Common class toxicity; weight, renal/cardiac context, and dose interruption matter
Creatinine rise May reflect transporter inhibition rather than true GFR loss; assess context
CNS disease Intracranial denominators are smaller than systemic cohorts
Resistance MET kinase-domain mutations and bypass signaling can require structural interpretation

On-target D1228 and Y1230 resistance substitutions can differ in sensitivity across type-I and type-II MET inhibitors. Foretinib showed preclinical activity against common capmatinib/tepotinib resistance mutations, but this is not yet a routine clinical sequence (Fujino 2022, PMID 35690785).

MET amplification after EGFR inhibition is a separate acquired-resistance state. Its copy-number threshold, focality, tissue-versus-plasma assay, and retained EGFR dependence determine whether combined EGFR–MET inhibition is rational; it should not be conflated with de novo METex14 disease.

HER2-mutant disease

HER2 in lung cancer has at least three biomarker states: activating mutation, amplification, and protein overexpression. Breast-cancer HER2 rules do not automatically transfer to lung adenocarcinoma.

DESTINY-Lung01 tested trastuzumab deruxtecan (T-DXd) in previously treated HER2-mutant NSCLC and reported ORR 55%, median response duration 9.3 months, and median PFS 8.2 months. Adjudicated drug-related interstitial lung disease occurred in 26%, including fatal events, making pulmonary monitoring inseparable from efficacy (Li 2022, PMID 34534430).

DESTINY-Lung02 compared 5.4 and 6.4 mg/kg dose cohorts. The lower dose preserved activity with a more favorable safety profile and became the clinically important dosing evidence (Goto 2023, PMID 37694347).

Zongertinib is an oral HER2-selective TKI designed to spare wild-type EGFR. In previously treated HER2-mutant NSCLC it showed substantial activity with a toxicity pattern distinct from ADC-related ILD and marrow toxicity (Heymach 2025, PMID 40293180).

HER2 strategy Strength Principal liability
T-DXd High response rate; bystander payload effect ILD/pneumonitis, nausea, cytopenias, cardiotoxicity
HER2-selective TKI Oral, mutation-directed, less wild-type EGFR inhibition Resistance durability and CNS evidence still maturing
Older pan-HER TKI Mechanistic plausibility Diarrhea/rash and limited efficacy
HER2 IHC-directed therapy Familiar biomarker IHC does not equal activating mutation in lung cancer

Cross-driver sequencing principles

  1. Confirm the exact actionable state before therapy.
  2. Prefer a genotype-matched agent when randomized evidence shows superiority over empiric systemic therapy.
  3. Record baseline CNS disease and use CNS-specific efficacy, not only systemic ORR.
  4. At progression, distinguish oligoprogression, on-target resistance, bypass resistance, and transformation.
  5. Re-biopsy only when the result can change management; combine tissue and plasma when feasible.
  6. Do not infer class-wide benefit from one allele or biomarker state.

Open questions

  • Which first-line combinations can deepen KRAS G12C responses without prohibitive hepatic or immune toxicity (PMIDs: 34096690, 36764316)?
  • Are STK11 and KEAP1 prognostic across treatments or prospectively predictive of a specific regimen (PMIDs: 29773717, 34740862)?
  • What is the optimal treatment for non-G12C KRAS alleles and non-V600 BRAF classes?
  • Can MET resistance genotyping produce a reproducible type-I/type-II inhibitor sequence (PMID 35690785)?
  • Does a HER2-selective TKI before or after T-DXd maximize lifetime CNS control and reduce ILD exposure (PMIDs: 37694347, 40293180)?
  • Which quantitative amplification threshold predicts benefit for MET or HER2 independently of mutation?

References

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  2. Skoulidis F, et al. Sotorasib for Lung Cancers with KRAS p.G12C Mutation. N Engl J Med. 2021. PMID 34096690
  3. de Langen AJ, et al. Sotorasib versus docetaxel for previously treated non-small-cell lung cancer with KRAS(G12C) mutation: a randomised, open-label, phase 3 trial. Lancet. 2023. PMID 36764316
  4. Jänne PA, et al. Adagrasib in Non-Small-Cell Lung Cancer Harboring a KRAS(G12C) Mutation. N Engl J Med. 2022. PMID 35658005
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