Kathy Pan1, Rowan T Chlebowski1, Joanne E Mortimer2, Marc J Gunter3, Thomas Rohan4, Mara Z Vitolins5, Lucile L Adams-Campbell6, Gloria Y F Ho7, Ting-Yuan David Cheng8, Rebecca A Nelson2. 1. The Lundquist Institute for Biomedical Innovation, Harbor-UCLA Medical Center, Torrance, California. 2. City of Hope National Medical Center, Duarte, California. 3. The International Agency for Research on Cancer, World Health Organization, Lyon, France. 4. Department of Epidemiology and Population Health, Albert Einstein College of Medicine, Bronx, New York. 5. Department of Epidemiology and Prevention, Wake Forest School of Medicine, Winston-Salem, North Carolina. 6. Georgetown University, Washington, DC. 7. Division of Epidemiology, Northwell Health, Great Neck, New York. 8. Department of Epidemiology, University of Florida at Gainesville, Gainesville, Florida.
Abstract
BACKGROUND: Insulin resistance is associated with higher all-cause and cancer-specific mortality in postmenopausal women. However, to the authors' knowledge, information regarding insulin resistance and breast cancer mortality risk is limited. Therefore, the authors examined associations between insulin resistance and breast cancer incidence and mortality in a subsample of Women's Health Initiative participants. METHODS: A total of 22,837 postmenopausal women with fasting baseline glucose and insulin levels were followed for incident breast cancer and breast cancer mortality. Breast cancers were verified by medical record review and serial National Death Index linkage-enhanced mortality findings. Insulin resistance was estimated using the homeostatic model assessment of insulin resistance (HOMA-IR). Multivariable Cox proportional hazards models were used to compute hazard ratios (HRs) with 95% confidence intervals (95% CIs) for quartile comparisons. Outcomes included breast cancer incidence, deaths from breast cancer, and deaths after breast cancer (breast cancer followed by death from any cause). RESULTS: During a median of 19.8 years of follow-up of 1328 breast cancer cases, there were 512 deaths reported, 151 of which were from breast cancer. Breast cancer incidence was higher in women in the highest HOMA-IR quartile (HR, 1.34; 95% CI, 1.12-1.61 [P for trend = .003]). Although HOMA-IR was not found to be associated with risk of death from breast cancer (HR, 1.04; 95% CI, 0.60-1.79), women in the highest versus those in the lowest HOMA-IR quartile were at a higher risk of death after breast cancer (HR, 1.78; 95% CI, 1.32-2.39 [P for trend <.001]). CONCLUSIONS: Higher levels of insulin resistance in postmenopausal women are associated with higher breast cancer incidence and higher all-cause mortality after breast cancer.
BACKGROUND:Insulin resistance is associated with higher all-cause and cancer-specific mortality in postmenopausal women. However, to the authors' knowledge, information regarding insulin resistance and breast cancermortality risk is limited. Therefore, the authors examined associations between insulin resistance and breast cancer incidence and mortality in a subsample of Women's Health Initiative participants. METHODS: A total of 22,837 postmenopausal women with fasting baseline glucose and insulin levels were followed for incident breast cancer and breast cancermortality. Breast cancers were verified by medical record review and serial National Death Index linkage-enhanced mortality findings. Insulin resistance was estimated using the homeostatic model assessment of insulin resistance (HOMA-IR). Multivariable Cox proportional hazards models were used to compute hazard ratios (HRs) with 95% confidence intervals (95% CIs) for quartile comparisons. Outcomes included breast cancer incidence, deaths from breast cancer, and deaths after breast cancer (breast cancer followed by death from any cause). RESULTS: During a median of 19.8 years of follow-up of 1328 breast cancer cases, there were 512 deaths reported, 151 of which were from breast cancer. Breast cancer incidence was higher in women in the highest HOMA-IR quartile (HR, 1.34; 95% CI, 1.12-1.61 [P for trend = .003]). Although HOMA-IR was not found to be associated with risk of death from breast cancer (HR, 1.04; 95% CI, 0.60-1.79), women in the highest versus those in the lowest HOMA-IR quartile were at a higher risk of death after breast cancer (HR, 1.78; 95% CI, 1.32-2.39 [P for trend <.001]). CONCLUSIONS: Higher levels of insulin resistance in postmenopausal women are associated with higher breast cancer incidence and higher all-cause mortality after breast cancer.