Response to Comment on: Yang et al. (2010) Associations of Hyperglycemia and Insulin Usage With the Risk of Cancer in Type 2 Diabetes: The Hong Kong Diabetes Registry. Diabetes;59:1254–1260

Abstract

We thank Carstensen (1) for his comments on our article published in the May issue of Diabetes (2). These comments have given us a chance to revisit some of the methodological issues in evaluating cancer risk associated with insulin use in type 2 diabetes. ### Cohort study designs. Carstensen suggests that analysis that considered all follow-up time in both the insulin-user group and the noninsulin-user group might produce more reliable results. In response to this, we estimated the hazard ratio (HR) of cancer with insulin use at or before enrollment or during follow-up in the entire cohort of 4,623 nonprevalent insulin users and 1,480 prevalent insulin users. Without adjusting for covariates, the cumulative incidences of cancer were similar in ever insulin users and nonusers (Fig. 1 A ). However, using the three adjustment schemes in the sensitivity analysis as reported in our article (2), the HRs were 0.68 (95% CI 0.51–0.91; P = 0.0085), 0.66 (0.49–0.88; P = 0.0047), and 0.65 (0.48–0.87; P = 0.0034), respectively. These results are consistent with our sensitivity analysis, which excluded prevalent insulin users, a point agreed on by Carstensen in his comment (1). In both analyses, either including or excluding prevalent insulin users, the follow-up time was calculated as the period of enrollment to the date of cancer, death, or censoring, whichever came first. In our sensitivity analysis, we did not exclude any follow-up time except for prevalent insulin users (Fig. 2). FIG. 1. Kaplan-Meier plots of cumulative incidence of cancer in insulin users and noninsulin users in type 2 diabetes. A : Cumulative incidence of cancer in prevalent insulin users and nonusers ( P from log-rank test = 0.3553). B : Cumulative incidence of cancer in new insulin users and nonusers in the sensitivity analysis ( P from log-rank test = 0.0075). C : Cumulative incidence of cancer in the new …