Insulin- and Obesity-Related Variables in Early-Stage Breast Cancer: Correlations and Time Course of Prognostic Associations
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PURPOSE: To investigate patterns of prognostic associations over time of insulin- and obesity-related variables measured at diagnosis of early breast cancer (BC), focusing on whether the prognostic associations with distant recurrence and death changed over time. PATIENTS AND METHODS: Five hundred thirty-five nondiabetic women with T1-3, N0-1, M0 invasive BC diagnosed from 1989 to 1996 were included in the study. Insulin-related variables included fasting insulin, Homeostasis Model Assessment, C-peptide, and glucose. Obesity-related variables included weight, body mass index (BMI), waist and hip circumference, and leptin. Correlations were examined using the Pearson correlation coefficient and prognostic associations using the Cox model. RESULTS: There was evidence that associations of baseline insulin-related variables with distant recurrence and death were not constant over time; univariable adverse prognostic associations were significant only during the first 5 years (eg, insulin quartile 4 v 1: hazard ratio [HR], 2.32; 95% CI, 1.39 to 3.86; P < .001 for distant disease-free survival [DDFS]; and HR, 2.85; 95% CI, 1.48 to 5.50; P = .002 for overall survival [OS], with little attenuation of this pattern in multivariable analyses). In contrast, obesity-related variables (BMI, weight, leptin) exerted significant adverse univariable associations that were constant over time (eg, BMI quartile 4 v 2: HR, 1.40; 95% CI, 1.07 to 1.82 for DDFS; P = .014; and HR, 1.50; 95% CI, 1.16 to 1.93; P < .001 for OS); prognostic associations of leptin remained significant in multivariable analyses. CONCLUSION: Baseline insulin- and obesity-related variables exert different patterns of prognostic associations over time in early BC.
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