For decades, the KRAS mutation was the specter haunting lung cancer oncology—a known driver of roughly a quarter of non-small cell lung cancers (NSCLC), yet stubbornly resistant to targeted therapy. That changed abruptly in 2021, when the first KRAS G12C inhibitor, sotorasib, received accelerated approval from the US Food and Drug Administration. Since then, a second agent, adagrasib, has joined the armamentarium, and the two drugs are forcing a rethinking of how we sequence therapy for patients with advanced NSCLC.

KRAS G12C Inhibitors Disrupt a Decades-Old Treatment Paradigm

Before KRAS G12C inhibitors, patients with KRAS-mutant NSCLC faced a treatment landscape that differed little from that of KRAS wild-type disease. Platinum-based chemotherapy remained the backbone of first-line therapy, often paired with immune checkpoint inhibitors for those with PD-L1 expression above a certain threshold. For patients whose tumors progressed, second-line options were limited to docetaxel—a drug with modest efficacy and considerable toxicity—or, for a subset, pemetrexed if not previously used.

The arrival of sotorasib and adagrasib changed the calculus. Both agents are oral small-molecule inhibitors that irreversibly bind to the mutant cysteine residue at position 12 of KRAS, locking the protein in its inactive GDP-bound state. In the pivotal CodeBreaK 200 trial, sotorasib improved median progression-free survival (PFS) compared with docetaxel (5.6 months vs 4.5 months; hazard ratio 0.66) in previously treated patients. Adagrasib, too, demonstrated a median PFS of 6.5 months in the KRYSTAL-1 trial. These results were sufficient for the National Comprehensive Cancer Network (NCCN) to list both agents as preferred second-line options for KRAS G12C-mutant NSCLC.

Yet the impact goes beyond second-line. As data accumulate, KRAS G12C inhibitors are beginning to move earlier in the treatment sequence, challenging the chemoimmunotherapy paradigm that has dominated first-line therapy for most of the past decade. Biomarker testing for KRAS G12C is now considered mandatory at diagnosis, because identifying the mutation early opens the door to a targeted approach that can delay or avoid chemotherapy.

Why KRAS G12C Was Called Undruggable and What Changed

The KRAS protein had long been considered undruggable for structural reasons. Unlike many kinases, KRAS is a small, globular GTPase with a relatively smooth surface and only shallow pockets. Its high affinity for guanine nucleotides makes it difficult to displace with a competitive inhibitor. For decades, efforts to target KRAS directly failed, leading many researchers to focus instead on downstream effectors like the MAPK pathway.

The breakthrough came in 2013, when a team led by Kevan Shokat at the University of California, San Francisco, solved the crystal structure of KRAS G12C bound to GDP. They discovered a cryptic pocket—the switch-II region—that is present only in the inactive GDP-bound state and is accessible to small molecules. The G12C mutation itself provided a unique foothold: the mutant cysteine could be targeted covalently, allowing irreversible binding.

Sotorasib, developed by Amgen, was the first to exploit this insight. It binds to the switch-II pocket and locks KRAS in the GDP-bound conformation, preventing activation by guanine nucleotide exchange factors. Adagrasib, from Mirati Therapeutics, uses a similar mechanism but was designed with an optimized half-life and better central nervous system penetration, which may matter for patients with brain metastases.

The clinical success of these drugs validated the approach and opened the door to a new class of agents. But the story is not one of unqualified triumph: response rates, though meaningful, are not durable in all patients, and acquired resistance emerges in a substantial fraction of cases within a year.

CodeBreaK 100 and 200: The Pivotal Trials That Altered Guidelines

The journey of sotorasib from bench to guideline began with CodeBreaK 100, an open-label, single-arm Phase 2 trial that enrolled 126 patients with KRAS G12C-mutant NSCLC who had received at least one prior systemic therapy. The objective response rate (ORR) was 37.1%, with a median duration of response of 11.1 months. These data, published in the New England Journal of Medicine in 2021, led to accelerated approval in the United States.

CodeBreaK 200, the confirmatory Phase 3 trial, randomized 345 patients in a 1:1 ratio to sotorasib or docetaxel. The study met its primary endpoint of PFS, with a hazard ratio of 0.66 (95% CI, 0.51–0.86). Median PFS was 5.6 months with sotorasib versus 4.5 months with docetaxel. Overall survival, however, did not reach statistical significance (median 10.6 vs 11.3 months; HR 1.01), a finding that some observers attribute to subsequent therapy crossover and the relatively small sample size.

Adagrasib's registration came via the KRYSTAL-1 trial, a Phase 2 study that reported a 42.9% ORR and a median PFS of 6.5 months in the efficacy-evaluable population. A randomized Phase 3 trial comparing adagrasib to docetaxel (KRYSTAL-12) is ongoing, but the existing data were sufficient for FDA accelerated approval in late 2022.

These trials collectively shifted the NCCN guidelines, which now list both sotorasib and adagrasib as preferred second-line options for KRAS G12C-mutant NSCLC. The European Society for Medical Oncology (ESMO) guidelines similarly recommend a KRAS G12C inhibitor after progression on platinum-based chemotherapy and an immune checkpoint inhibitor.

First-Line Combinations Challenge Chemoimmunotherapy Dominance

The natural next question was whether KRAS G12C inhibitors could be used in the first-line setting, either alone or in combination with other agents. Early data are encouraging but tempered by toxicity concerns.

The CodeBreaK 101 trial investigated sotorasib plus pembrolizumab in a Phase 1b expansion cohort of 58 patients with previously untreated KRAS G12C-mutant NSCLC. The ORR was 29% among those with PD-L1 tumor proportion score less than 50%, and 57% in the overall population. However, a signal of dose-limiting hepatotoxicity emerged: grade 3 or higher elevations in alanine aminotransferase (ALT) occurred in roughly 15% of patients, leading to a protocol amendment that reduced the sotorasib dose in the combination.

Adagrasib plus pembrolizumab, tested in the KRYSTAL-7 trial, showed an ORR of 39% in the first-line population, with a safety profile that also included liver enzyme elevations. The combination is being further evaluated in the Phase 3 KRYSTAL-17 trial, which randomizes patients to adagrasib plus pembrolizumab versus chemotherapy plus pembrolizumab.

For now, the standard first-line approach remains chemoimmunotherapy for most patients with KRAS G12C-mutant NSCLC, particularly those with PD-L1 expression below 50%. But the trend is clear: as combination regimens mature and toxicity management improves, KRAS G12C inhibitors may eventually supplant chemotherapy in the first line for biomarker-selected populations.

Acquired Resistance Mechanisms Demand Sequential Strategies

No targeted therapy is immune to resistance, and KRAS G12C inhibitors are no exception. Resistance emerges through multiple mechanisms, some of which are already well characterized.

Secondary mutations in KRAS itself can prevent drug binding. The most common include Y96D, which alters the switch-II pocket, and H95R, which affects the binding site directly. These mutations can be detected by liquid biopsy at the time of progression, offering a window into the mechanism of resistance.

More frequently, resistance arises through reactivation of the MAPK pathway via mutations in NRAS, BRAF, or the receptor tyrosine kinases (e.g., EGFR, MET). Preclinical models suggest that combining a KRAS G12C inhibitor with a MEK inhibitor or a SHP2 inhibitor may suppress these escape routes. Early clinical trials, such as the combination of adagrasib with the MEK inhibitor trametinib, are under way, though tolerability is a concern.

For clinicians, the practical implication is that sequential therapy—starting with a KRAS G12C inhibitor, then switching to chemotherapy or other targeted agents upon progression—may not be optimal if resistance is polyclonal or driven by bypass signaling. Instead, combination strategies from the start may be necessary, though they come with added toxicity and cost.

Liquid biopsy surveillance is becoming a routine tool to monitor for resistance mutations. A recent study found that circulating tumor DNA (ctDNA) can detect emerging resistance mutations weeks before radiographic progression, potentially allowing early intervention. However, the clinical utility of such preemptive switching has not yet been proven in randomized trials.

Practical Takeaways for Clinicians Managing Sequencing

The shifting landscape has immediate implications for how clinicians approach a new diagnosis of advanced non-squamous NSCLC. First and foremost, testing for KRAS G12C—along with other actionable biomarkers such as EGFR, ALK, and PD-L1—should be performed at diagnosis, not deferred until after first-line therapy. A tumor tissue sample or a liquid biopsy can provide the necessary genotyping.

For patients whose tumors harbor KRAS G12C, the current standard is still first-line platinum-based chemotherapy plus an immune checkpoint inhibitor, regardless of PD-L1 status. After progression, a KRAS G12C inhibitor is a well-supported second-line option. Some clinicians may consider using the inhibitor in the first line for patients who are not candidates for chemotherapy, but this remains off-label in most settings and is not supported by randomized data.

When prescribing a KRAS G12C inhibitor, clinicians should monitor for interstitial lung disease (ILD)—a rare but serious adverse event—and regularly check liver function tests. Hepatotoxicity is the most common grade 3 or higher toxicity, and it can be managed with dose interruption or reduction, though it may require discontinuation in some cases.

The emergence of resistance is expected; repeat biopsy or liquid biopsy at progression can help guide next-line choices. If a secondary KRAS mutation is found, switching to a different KRAS G12C inhibitor is unlikely to be effective, and the patient should be transitioned to chemotherapy or a clinical trial. If no acquired mutation is detected, continuation of the inhibitor beyond progression, often in combination with chemotherapy, is sometimes used but lacks robust evidence.

Cost and access remain barriers. KRAS G12C inhibitors are expensive, and prior authorization requirements can delay therapy. A recent analysis found that formulary step therapy delays lung cancer therapy by six weeks in some cases, a delay that can allow tumors to progress. Clinicians should be prepared to advocate for timely access and to consider patient assistance programs.

Finally, it is worth remembering that KRAS G12C inhibitors are not curative. They extend PFS by a few months in the second-line setting and may offer longer benefit in the first line, but resistance eventually emerges. The field is moving toward combination strategies that target multiple nodes of the MAPK pathway simultaneously, and toward next-generation inhibitors that may overcome some resistance mutations. Until those arrive, careful sequencing and monitoring remain the best tools we have.

Ongoing Trials and Future Directions

Several ongoing trials are exploring novel combinations and next-generation inhibitors. The CodeBreaK 300 trial is evaluating sotorasib in combination with the MEK inhibitor trametinib versus docetaxel in second-line, with results expected in 2025. Similarly, the KRYSTAL-14 trial is testing adagrasib plus the SHP2 inhibitor RMC-4630, aiming to block adaptive resistance mechanisms. Early-phase data suggest that dual inhibition of KRAS and SHP2 can delay resistance in preclinical models, but clinical translation is still pending.

Beyond sotorasib and adagrasib, several next-generation KRAS G12C inhibitors are in development. For example, RMC-6291 is a tri-complex inhibitor that binds to both KRAS G12C and cyclophilin A, creating a more stable interaction. In a Phase 1 trial, RMC-6291 showed a 40% ORR in heavily pretreated patients, including some who had progressed on sotorasib or adagrasib. Another agent, JDQ443, is being developed by Novartis and has shown a 57% ORR in a Phase 1 trial at the recommended dose. These newer agents may offer improved efficacy or activity against certain resistance mutations.

Another area of active investigation is the use of KRAS G12C inhibitors in earlier stages of disease. The CodeBreaK 1000 trial is evaluating sotorasib as adjuvant therapy after surgical resection in stage IB-IIIA NSCLC. While results are not yet available, the concept is appealing: targeting the driver mutation with a well-tolerated oral agent could reduce the risk of recurrence. However, the potential for long-term toxicity and the emergence of resistance in the adjuvant setting remain concerns.

Combinations with immunotherapy continue to be refined. The KEYNOTE-811 trial, which tested pembrolizumab plus trastuzumab in HER2-positive gastric cancer, set a precedent for combining targeted therapy and immunotherapy, but the hepatotoxicity seen with sotorasib plus pembrolizumab suggests that careful dose optimization is needed. Alternative approaches, such as sequential rather than concurrent administration, are being explored in preclinical models. For instance, giving a KRAS G12C inhibitor after a short course of immunotherapy may allow for immune priming without overlapping toxicity.

Finally, the role of KRAS G12C inhibitors in patients with brain metastases is gaining attention. Adagrasib has demonstrated CNS penetration, with intracranial response rates of 33% in a subset of patients with untreated brain metastases in the KRYSTAL-1 trial. Sotorasib has lower CNS penetration, but newer formulations or next-generation inhibitors may improve intracranial activity. For patients with brain metastases, adagrasib may be preferred, though prospective comparisons are lacking.

In summary, the landscape for KRAS G12C-mutant NSCLC is evolving rapidly. While current guidelines still position these inhibitors in the second line, accumulating evidence from combination trials and next-generation agents may soon support their use in first-line and even adjuvant settings. Clinicians must stay informed about emerging data, maintain a low threshold for biomarker testing, and engage in shared decision-making with patients about the trade-offs between efficacy, toxicity, and cost.

This article is for informational purposes only and does not constitute personalized medical advice. Treatment decisions should be made in consultation with a qualified healthcare professional.