Fracture and osteoporosis are known side effects of aromatase inhibitors (AIs) for postmenopausal hormone receptor positive (HR+) breast cancer (BC) patients. How modifiable lifestyle factors impact fracture risk in these patients is relatively unknown.
Methods
We conducted a prospective cohort study to examine the association of lifestyle factors, focusing on physical activity, with risk of incident major osteoporotic fracture and osteoporosis in 2152 HR+ BC patients diagnosed from 2006 to 2013 at Kaiser Permanente Northern California and who received AIs. Patients self-reported lifestyle factors at study entry and at 6-month follow-up. Fracture and osteoporosis outcomes were prospectively ascertained by physician-adjudication and bone mineral density (BMD) values, respectively. Hazard ratios (HRs) and 95% confidence intervals (CIs) were calculated from multivariable proportional hazards regression. Models were adjusted for age, menopausal status, race/ethnicity, body mass index (BMI), AJCC stage, breast cancer treatment, prior osteoporosis, and prior major fracture.
Results
Over a median 6.1 years of follow-up after AI initiation, 165 women experienced an incident osteoporotic fracture and 243 women had osteoporosis. No associations were found between overall moderate-vigorous physical activity and fracture risk, although < 150 min/week of aerobic exercise in the 6 months after BC diagnosis was associated with increased fracture risk (HR=2.42; 95% CI: 1.34, 4.37) compared with ≥ 150 min/week (meeting physical activity guidelines). Risk was also higher for never or infrequently engaging in aerobic exercise (HR=1.90; 95% CI: 1.05, 3.44). None or infrequent overall moderate-vigorous physical activity in the 6 months before BC diagnosis was associated with increased risk of osteoporosis (HR=1.94; 95% CI: 1.11; 3.37).
Conclusions
Moderate-vigorous physical activity during the immediate period after BC diagnosis, particularly aerobic exercise, was associated with lower risk of major osteoporotic fractures in women on AI therapy.