The FDA has granted accelerated approval to a combination of MRTX1133 (a KRAS G12D inhibitor) and nivolumab (PD-1 checkpoint blockade) for first-line treatment of metastatic pancreatic ductal adenocarcinoma (PDAC) with confirmed KRAS G12D mutation — doubling median overall survival from 11.2 to 22.0 months in the pivotal Phase 3 BREAKTHROUGH-PDAC trial.

Why Pancreatic Cancer Has Been So Hard to Treat

Pancreatic ductal adenocarcinoma is the fourth leading cause of cancer death in high-income countries, despite being only the 13th most common cancer by incidence. Its outsized lethality reflects two fundamental biological characteristics: it is rarely caught before metastasis, and it has been essentially immune to immunotherapy due to its densely immunosuppressive tumour microenvironment — characterised by a thick stromal barrier, sparse T-cell infiltration, and extremely low tumour mutational burden.

KRAS mutations drive approximately 95% of all pancreatic cancers. The G12D variant — present in 39% of PDAC cases — has been considered “undruggable” for decades due to the absence of a suitable binding pocket on the KRAS protein.

The KRAS Breakthrough

MRTX1133, developed by Mirati Therapeutics (now acquired by Bristol Myers Squibb), is the first potent and selective KRAS G12D inhibitor to reach Phase 3. It works by locking the mutant KRAS protein in an inactive GDP-bound state, preventing downstream RAS-MAPK and PI3K-AKT signalling that drives tumour proliferation.

Preclinical work showed that KRAS G12D inhibition increases T-cell infiltration into PDAC tumours by 4–6 fold — transforming cold tumours into hot ones potentially susceptible to checkpoint blockade. This was the scientific rationale for combining MRTX1133 with nivolumab.

BREAKTHROUGH-PDAC Trial Results

1,247 patients with previously untreated metastatic PDAC and confirmed KRAS G12D mutation were randomised to MRTX1133 + nivolumab vs gemcitabine/nab-paclitaxel (standard of care):

  • Median overall survival: 22.0 months (combination) vs 11.2 months (SOC) — HR 0.46, P<0.001
  • 1-year survival rate: 72% vs 43%
  • 2-year survival rate: 41% vs 18%
  • Objective response rate: 44% vs 26%

“Doubling survival in pancreatic cancer is something I would have called impossible five years ago. This combination has cracked open a disease that has defeated every treatment we have thrown at it.”

— Dr. Eileen O’Reilly, Memorial Sloan Kettering Cancer Center, principal investigator

Access and Testing

The approval requires prior KRAS G12D mutation testing via an FDA-approved companion diagnostic. The combination carries a list price of approximately $28,000 per month. Oncologists note that KRAS G12D testing — performed on tumour biopsy tissue or liquid biopsy — is not yet uniformly available in low-resource settings, including much of rural India where pancreatic cancer is significantly underdiagnosed.

⚕️ Medical Disclaimer: This article is for informational purposes only. It does not constitute medical advice. Always consult a qualified healthcare professional before making health decisions.