Additive interaction of diabetes mellitus and chronic kidney disease in cancer patient mortality risk.

We investigated the additive interaction of diabetes mellitus (DM) and chronic kidney disease (CKD) on the risk of mortality in cancer patients and evaluated the impact of diabetic kidney disease (DKD) on mortality in cancer patients with DM. We retrospectively analyzed 101,684 cancer patients. A multivariable Cox regression model was used for assessing mortality risk. Relative excess risk due to interaction (RERI), attributable proportion (AP), and synergy index (SI) were used to evaluate the additive interactive effect. The adjusted hazard ratio (aHR, 95%CI) for mortality was significant for those with CKD alone (1.53, 1.39-1.68), DM alone (1.25, 1.2-1.3), and both CKD and DM (1.99, 1.84-2.17) compared to non-CKD and non-DM cancer patients. The additive interaction between CKD and DM was significant (RERI 0.22[95%CI = 0.01-0.42], AP 0.11[0.01-0.21], SI 1.28[1.01-1.62]). Among cancer patients with DM, the presence of DKD raised the aHR for mortality (1.55, 95%CI = 1.33-1.81) compared to those without DKD. Coexistence of DM and CKD at the time of cancer diagnosis was significantly associated with an increased risk of mortality, and their interaction exerted an additive interactive effect on mortality. DKD was significantly associated with an increased risk of mortality in cancer patients with DM.