To investigate the associations of diabetes mellitus with recurrence and prognosis after surgery for non-metastatic renal cell carcinoma and the effect modification of obesity on the above relationships.Methods
We retrospectively evaluated 543 patients with non-metastatic renal cell carcinoma (pT1-4N0M0) who underwent radical or partial nephrectomy. The association of diabetes mellitus with recurrence was analyzed using the Kaplan–Meier method and the Cox regression model. We also examined whether the above relationships were modified by obesity using subgroup analysis and tests of interaction. For subgroup analysis, the body mass index was categorized as non-obese (<25 kg/m2) and obese (≥25 kg/m2).Results
Eighty-two patients (15.1%) had a history of diabetes mellitus. During the mean follow-up of 66.7 months, 68 patients (12.5%) developed recurrence. Although the body mass index was not associated with recurrence, diabetes mellitus was an independent predictor of recurrence in multivariate analysis (hazard ratio 2.43, P = 0.003), along with tumor diameter, grade and pathological T stage. In further subgroup analysis, the same relationship between diabetes mellitus and recurrence was clearly shown in the obese group (hazard ratio 4.07, P = 0.010), but not in the non-obese group (hazard ratio 1.95, P = 0.125). At the same time, obesity modified the effect of diabetes mellitus on recurrence with a trend (P-interaction = 0.086). In the obese group, 5-year recurrence-free survival rates were 75.3 and 91.9% for diabetes mellitus and non-diabetes mellitus patients, respectively (P < 0.001). Restricting analyses to patients with clear cell type histology did not materially change these results.Conclusions
Diabetes mellitus is a predictor of recurrence following surgery for non-metastatic renal cell carcinoma, especially in obese patients.