The impact of KRAS mutations on the clinical outcome and immune response following immunotherapy for pancreatic cancer

Background: Pancreatic ductal adenocarcinoma (PDAC) is predicted to be the second leading cause of cancer-related death by 2030. This is driven by a high case-fatality rate with most patients even with radiologically localized PDAC at diagnosis ultimately relapsing with metastatic disease. KRAS mutations present in 90% to 95% of PDAC drive these poor statistics through its role in driving cellular growth, inhibition of apoptosis, and immunosuppression. The recent development of KRAS inhibitors has increased interest in understanding key molecular differences between the different KRAS codon changes seen in PDAC and other malignancies and how this might alter therapeutic decision making.

Methods: To understand how mutant KRAS influences the PDAC tumor microenvironment (TME) and cytokine signaling, we evaluated patients enrolled on NCT02451982 (A Platform Study of Combination Immunotherapy for the Neoadjuvant and Adjuvant Treatment of Patients with Surgically Resectable Adenocarcinoma of the Pancreas). Interleukin 8 levels were measured using ELISA, these levels were compared with previously determined KRAS mutation status using next generation sequencing, tumor immune microenvironment populations quantified using multiplex immunohistochemistry, and survival outcomes.

Results: We identified a total of 30 patients from cohorts A: GVAX, an allogeneic whole cell cancer vaccine (n=16) and B: GVAX + anti-PD-1 (nivolumab) (n=14) with known KRAS mutation status and survival outcomes. Twenty-six of these tumors were KRAS mutant (G12C: 1, G12D: 11, G12R: 4, G12V: 10) and four were KRAS wild type. As KRAS G12D was the most commonly identified mutation and has been associated in some cohorts with worse outcomes, this was evaluated as a separate subgroup. KRAS G12D mutant PDAC had decreased disease-free survival (P=0.01) and a trend towards inferior overall survival in patients treated with GVAX alone (P=0.14) or GVAX plus anti-PD-1 (P=0.17) which became significant when combining both treatment groups (P=0.04). Looking at the relationship between KRAS status and the immune composition of the TME, patients with KRAS mutant PDAC had a trend towards decreased CD8⁺ T lymphocyte (P=0.06) following treatment with GVAX compared to KRAS wild type tumors. With the addition of anti-PD-1 in Arm B, patients with KRAS G12D mutant disease had a lower ratio of CD8⁺ GZMB⁺/CD8⁺ T lymphocytes (P=0.005).

Conclusions: KRAS G12D mutated PDAC represents a unique subtype of disease with decreased survival and lower ratio of activated CD8⁺ T lymphocytes as denoted by granzyme B (GZMB) positivity following GVAX/aPD-1 treatment.