KRAS G12C Inhibitors: Clinical Progress, Resistance Mechanisms, and Next-Generation Therapeutic Strategies (2021–July 2026)

Background and Rationale

Kirsten rat sarcoma viral oncogene homologue (KRAS) mutations represent the most frequently altered oncogene across solid tumors, occurring in approximately 35% of non-small cell lung cancers (NSCLCs), 45% of colorectal cancers (CRCs), and up to 90% of pancreatic ductal adenocarcinomas (PDACs). For decades, KRAS was deemed undruggable owing to its smooth surface and the absence of suitable pharmacological binding pockets. The discovery of a switch II allosteric pocket in the inactive, GDP-bound KRAS G12C isoform—containing a cysteine residue uniquely amenable to irreversible covalent modification—enabled the rational design of selective inhibitors and fundamentally transformed the therapeutic landscape 127. Between 2021 and July 2026, two first-generation agents achieved regulatory approval, multiple next-generation compounds entered late-stage development, and resistance mechanisms were systematically characterized. This review synthesizes pivotal trial data, regulatory milestones, resistance biology, and emerging combination strategies for an audience of oncologists, oncology pharmacists, and translational researchers.

Approved Agents and Regulatory Milestones

Sotorasib (Lumakras/Lumykras; Amgen) became the first approved KRAS G12C inhibitor, receiving U.S. Food and Drug Administration (FDA) approval on 28 May 2021 for previously treated advanced NSCLC harboring KRAS G12C mutations. The European Medicines Agency (EMA) granted conditional marketing authorization on 6 January 2022, based on the CodeBreaK 100 Phase II trial (n=124–126), which demonstrated an objective response rate (ORR) of 37.1% (95% CI: 28.6–46.2%), median duration of response (DoR) of 11.1 months, and median progression-free survival (PFS) of 6.8 months 1427. In the Phase III CodeBreaK 200 trial comparing sotorasib with docetaxel in second-line NSCLC, sotorasib yielded superior ORR (28.1% vs. 13.2%) and PFS (5.6 vs. 4.5 months; HR 0.66; P=0.0017), though no overall survival (OS) advantage was observed 27. On 16 January 2025, the FDA approved sotorasib in combination with panitumumab (an anti-epidermal growth factor receptor [EGFR] monoclonal antibody) for KRAS G12C–mutated metastatic CRC (mCRC), following the earlier approval of adagrasib plus cetuximab for the same indication 161.

Adagrasib (Krazati; Bristol-Myers Squibb/Mirati) received FDA accelerated approval on 12 December 2022 for previously treated KRAS G12C–positive NSCLC, and EMA conditional approval on 5 January 2024 15. The KRYSTAL-1 Phase I/II trial (n=116) demonstrated an ORR of 41.4–42.9%, median DoR of 8.5 months, median PFS of 6.5 months, and median OS of 12.6 months in advanced NSCLC 27. Adagrasib showed notable intracranial activity: in patients with NSCLC and brain metastases, an intracranial ORR of 42%, intracranial disease control rate (DCR) of 90%, and intracranial PFS of 5.4 months were reported 27. On 21 June 2024, the FDA granted accelerated approval to adagrasib plus cetuximab for previously treated KRAS G12C–mutated mCRC; in the KRYSTAL-1 CRC cohort, adagrasib monotherapy achieved an ORR of 22% and DCR of 87%, rising to ORR 43% and DCR 100% when combined with cetuximab 30.

Glecirasib (JAB-21822; Jacobio Pharma) received China National Medical Products Administration (NMPA) approval in 2025 for KRAS G12C–mutated NSCLC with at least one prior systemic therapy, based on a multicenter Phase IIb trial (n=117) demonstrating a confirmed ORR of 47.9% (including 4 complete responses), DCR of 86.3%, median PFS of 8.2 months, and median OS of 13.6 months, with a favorable safety profile (grade 3–4 treatment-related adverse events [TRAEs] in 38.7%; no treatment-related deaths) 2021. Glecirasib was subsequently included in China's National Reimbursement Drug List (NRDL) in 2025 21.

Table 1. Global Development and Regulatory Status of Major KRAS G12C Inhibitors (as of July 24, 2026)

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Key Clinical Trial Outcomes

Table 2. Pivotal Clinical Trial Outcomes by Drug, Tumor Type, and Therapy Line

Abbreviations: 1L first-line; 2L+ second-line or beyond; 3L+ third-line or beyond; DCR disease control rate; GI gastrointestinal; mo months; mCRC metastatic CRC; NR not reported in retrieved materials; ORR objective response rate; OS overall survival; PDAC pancreatic ductal adenocarcinoma; PFS progression-free survival; SHP2i SHP2 inhibitor; SOC standard of care; TRAEs treatment-related adverse events.

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Resistance Mechanisms and Corresponding Therapeutic Strategies

Despite meaningful clinical activity in NSCLC, durability of response to KRAS G12C inhibitors is limited, with median PFS ranging from 5.6 to 13.1 months across monotherapy cohorts. Understanding resistance is therefore critical 273839.

Primary resistance affects approximately 36% of sotorasib-treated patients (defined as PFS <3 months) and is associated with co-mutations in KEAP1/NRF2, STK11/LKB1, SMARCA4, and CDKN2A 2723. Integrated biomarker analyses of CodeBreaK 100/200 demonstrated that KEAP1-mutant tumors had significantly shorter PFS and OS with sotorasib, and NRF2 High tumors showed markedly inferior outcomes (median PFS 2.73 vs. 7.75 months; median OS 6.05 vs. 16.0 months) compared with NRF2 Low tumors. TTF-1 expression emerged as a robust stratifier: TTF-1 Low tumors treated with sotorasib achieved an ORR of only 4.17% versus 42.1% in TTF-1 High tumors 23. In CRC, intrinsic resistance is attributable to high basal receptor tyrosine kinase (RTK) activity and elevated EGFR-mediated feedback reactivation of the MAPK (mitogen-activated protein kinase) pathway, explaining the substantially lower monotherapy ORR in CRC versus NSCLC 93233.

Acquired resistance emerges through multiple convergent mechanisms. In vitro analysis of 142 Ba/F3 clones resistant to sotorasib or adagrasib identified 12 distinct secondary KRAS mutations in 87% of resistant clones; Y96D and Y96S conferred cross-resistance to both agents, while G13D, R68M, A59S, and A59T were resistant to sotorasib but remained sensitive to adagrasib, suggesting potential for sequential inhibitor use 34. Clinical ctDNA analyses identified MET amplification (30%) and EGFR amplification (20%) as frequent acquired alterations, underscoring RTK pathway remodeling as a dominant escape mechanism 23. Single-patient autopsy-based analysis of sotorasib-resistant tumors revealed concurrent activation of KRAS-mediated signaling, metabolic reprogramming, epithelial–mesenchymal transition (EMT), and tumor microenvironment remodeling 40. In CRC and PDAC, pre-existing putative resistance alterations in EGFR, BRAF, and MAP2K1 were identified in 16.4–53.8% of KRAS G12C cases, correlating with inferior OS in CRC 28.

Table 3. Acquired Resistance Mechanisms and Therapeutic Strategies

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Next-Generation Strategies and Emerging Combinations

The most clinically significant advance in the 2025–2026 period was the Krascendo 1 Phase III trial, in which divarasib demonstrated statistically significant and clinically meaningful improvements in both PFS and OS compared with first-generation sotorasib or adagrasib in 338 patients with previously treated KRAS G12C–mutant advanced NSCLC—representing the first head-to-head Phase III superiority demonstration in this class 17. The Krascendo 170 Phase Ib/II study evaluated divarasib plus pembrolizumab in first-line KRAS G12C–mutant NSCLC (ASCO 2026 data), and the Phase III Krascendo 2 trial is actively enrolling to compare this chemotherapy-free combination with chemoimmunotherapy in the first-line setting 18.

Olomorasib showed a particularly important property: activity in patients previously treated with a KRAS G12C inhibitor (ORR 41–42%, median PFS 8.1–8.2 months), alongside preliminary intracranial activity (>30% lesion reduction in 6 of 9 evaluable patients with untreated active brain metastases) 3. In the SUNRAY-01 program, olomorasib plus pembrolizumab achieved an ORR of 77% in first-line metastatic NSCLC, and an integrated analysis with chemoimmunotherapy demonstrated ORR of 61% with DCR of 90% across all PD-L1 expression levels 319.

Elisrasib received FDA Fast Track and Breakthrough Therapy designations for second-line KRAS G12C inhibitor-naive NSCLC. In a Phase I/II update at AACR 2026, elisrasib 600 mg in inhibitor-naive patients achieved ORR 58.8%, DCR 98.5%, median PFS 12.2 months, median DoR 16.5 months, and a 12-month OS rate of 72%, with grade ≥3 TRAEs in only 11.5%. Importantly, elisrasib also retained activity in prior KRAS G12C inhibitor-refractory NSCLC (ORR 32.3%, median PFS 8.1 months) 8.

SHP2 (Src homology 2 domain-containing phosphatase-2) inhibition targets RTK-mediated KRAS reactivation upstream. The combination of glecirasib with the SHP2 inhibitor sitneprotafib achieved an ORR of 71% and median PFS of 12.2 months in first-line NSCLC, with a registrational Phase III trial ongoing in China 21. SOS1 (son of sevenless homologue 1) inhibitors, such as BI-3406, block GDP-to-GTP exchange and demonstrate preclinical activity against Y96D/S resistance mutations when combined with trametinib 34. Beyond NSCLC, KRAS G12D inhibitors (HRS-4642, INCB161734) showed early activity in PDAC at ESMO 2025, with ORRs of 20–34% in PDAC cohorts at higher doses, addressing the dominant KRAS mutation in pancreatic cancer 26.

In PDAC specifically, KRAS G12C monotherapy with adagrasib or sotorasib has shown ORRs of approximately 21–33% and PFS of 4.0–5.4 months—meaningful but inferior to NSCLC—likely reflecting a dense immunosuppressive stroma and high prevalence of pre-existing resistance alterations (16.4–36.4% of KRAS G12C PDAC cases) 24252829.

Remaining Clinical Challenges

Several challenges require prospective resolution. First, durability remains limited for monotherapy; median PFS of 5.6–13.1 months necessitates combination approaches. Second, while adagrasib and olomorasib have demonstrated intracranial activity signals, CNS penetration is incompletely characterized for most agents, with no mature randomized intracranial efficacy data retrieved in the reviewed materials 310. Third, tumor-type differences are substantial: CRC responds poorly to monotherapy and mandates EGFR co-targeting, while PDAC responses are modest and require novel combination design. Fourth, optimal sequencing of KRAS G12C inhibitors—particularly given the distinct secondary mutation profiles relevant to sequential therapy—requires prospective validation 34. Fifth, biomarker-guided patient selection based on TTF-1 expression, NRF2 pathway status, KEAP1/STK11 co-mutations, and early ctDNA dynamics (KRAS G12C clearance by cycle 1/day 8 correlated with improved PFS) offers a framework for treatment individualization, but requires prospective integration into trial design 23. Finally, rational combination trial design informed by mechanistic resistance biology—rather than empirical doublet construction—will be essential to maximize clinical benefit and avoid overlapping toxicity.

The period from 2021 to July 2026 has witnessed a transformation from first-in-class proof of concept to Phase III superiority demonstration and first-line combination exploration. As next-generation agents, SHP2/SOS1 pathway combinations, immunotherapy pairings, and KRAS G12D inhibitors mature, biomarker-stratified and sequencing-optimized approaches will define the next standard of care for KRAS G12C–driven malignancies.