Influence of dietary insulin scores on survival in patients with metastatic colorectal cancer (mCRC): Findings from CALGB (Alliance) 80405

3568 Background: Diets inducing an elevated insulin response have been associated with increased recurrence and mortality in patients with non-metastatic colorectal cancer, but it remains unknown if postprandial hyperinsulinemia also affects progression and mortality in mCRC patients. The goal of this study was to assess the influence of dietary insulin load (DIL) and dietary insulin index (DII) on survival of mCRC patients. Methods: This was a prospective cohort study of 1,177 patients with previously untreated mCRC enrolled in a phase III trial of systemic chemotherapy plus biologics who reported dietary intake within one month after chemotherapy initiation. DIL was calculated as a function of food insulin index and the energy content of individual foods reported on a food frequency questionnaire. DII was calculated by dividing DIL by total energy intake. The primary endpoint was overall survival (OS). Secondary endpoints were progression-free survival (PFS) and treatment-related adverse events (TRAEs). The primary statistical test was a test for trend, which was performed using the median value for each quintile of dietary insulin score as a continuous variable. Cox proportional hazards regression was used to adjust for potential confounders including assigned treatment arm, known prognostic factors, comorbidities, body mass index, and physical activity. Results: Higher DIL was significantly associated with worse OS (ptrend = 0.04); patients in the highest quintile survived 34.1 months, compared to 27.7 months in the lowest quintile (Cox hazard ratio [HR] 1.22, 95% confidence interval [CI] 0.99 - 1.51). Higher DII was non-significantly associated with worse OS (HR 1.18, 95% CI 0.94 - 1.48, ptrend = 0.09). There was no significant association between dietary insulin scores and PFS. The influence of dietary insulin scores on survival did not differ significantly by various molecular markers involved in the insulin signaling pathway, including C-peptide, adiponectin, IGF-1, IGFBP-3, and IGFBP-7. Higher dietary insulin scores were significantly associated with greater risk of any TRAE. Those with a DIL greater than the median had a 75.4% rate of any TRAE, compared to 70.8% in those with a DIL less than or equal to the median (HR 1.19, 95% CI 1.03 - 1.38, p=0.02); the most significant associations were with neutropenia (HR 1.30, 95% CI 1.05 - 1.61, p=0.01) and diarrhea (HR 1.43, 95% CI 1.00 - 2.06, p=0.05). Conclusions: Higher DIL was significantly associated with worse OS, and both higher DIL and DII were significantly associated with increased TRAEs, in patients with previously untreated mCRC. These findings may inform future dietary recommendations for patients with mCRC. Further investigation into the molecular mechanisms underlying these associations is warranted. Clinical trial information: NCT00265850.