The association between endocrine therapy use and osteoporotic fracture among post-menopausal women treated for early-stage breast cancer in Ontario, Canada
Phillip S. Blanchette,
Melody Lam,
Britney Le,
Lucie Richard,
Salimah Z. Shariff,
Alexandra M. Ouédraogo,
Kathleen I. Pritchard,
Jacques Raphael,
Ted Vandenberg,
Ricardo Fernandes,
Danielle N. Desautels,
Kelvin K.W. Chan,
Craig C. Earle
Affiliations
Phillip S. Blanchette
Division of Medical Oncology, London Regional Cancer Program, London Health Sciences Centre, University of Western Ontario, London, Ontario, Canada; ICES Western, London, Ontario, Canada; Corresponding author. Division of Medical Oncology, London Regional Cancer Program, University of Western Ontario, 800 Commissioners Road East, London, Ontario, N6A 5W9, Canada.
Melody Lam
ICES Western, London, Ontario, Canada
Britney Le
ICES Western, London, Ontario, Canada
Lucie Richard
ICES Western, London, Ontario, Canada
Salimah Z. Shariff
ICES Western, London, Ontario, Canada
Alexandra M. Ouédraogo
ICES Western, London, Ontario, Canada
Kathleen I. Pritchard
Division of Medical Oncology, Sunnybrook Odette Cancer Centre, University of Toronto, Toronto, Ontario, Canada
Jacques Raphael
Division of Medical Oncology, London Regional Cancer Program, London Health Sciences Centre, University of Western Ontario, London, Ontario, Canada; ICES Western, London, Ontario, Canada
Ted Vandenberg
Division of Medical Oncology, London Regional Cancer Program, London Health Sciences Centre, University of Western Ontario, London, Ontario, Canada
Ricardo Fernandes
Division of Medical Oncology, London Regional Cancer Program, London Health Sciences Centre, University of Western Ontario, London, Ontario, Canada
Danielle N. Desautels
CancerCare Manitoba Research Institute, University of Manitoba, Winnipeg, Manitoba, Canada
Kelvin K.W. Chan
Division of Medical Oncology, Sunnybrook Odette Cancer Centre, University of Toronto, Toronto, Ontario, Canada; Canadian Centre for Applied Research in Cancer Control, Toronto, Ontario, Canada
Craig C. Earle
Division of Medical Oncology, Sunnybrook Odette Cancer Centre, University of Toronto, Toronto, Ontario, Canada; ICES, University of Toronto, Toronto, Ontario, Canada
Background: The use of endocrine therapy for early-stage breast cancer, particularly aromatase inhibitor therapy has been associated with an increased risk of osteoporosis and fracture in clinical trials. We sought to validate this observation in real-world practice. Methods: We used health administrative data collected from post-menopausal women (aged ≥66 years) who were diagnosed with breast cancer and started on adjuvant endocrine therapy from 2005 to 2012. Patients were classified by use of either an aromatase inhibitor or tamoxifen and followed until 2017 for a new diagnosis of an osteoporotic fracture. A multivariable analysis using a Cox proportional hazards model was adjusting for age, medical co-morbidities, medication use and duration of endocrine therapy. Results: We identified 12,077 patients of whom 73% were treated with an aromatase inhibitor as compared to 27% with tamoxifen. Our multivariable analysis did not demonstrate any significant difference in the rate of osteoporotic fracture between patients treated with an aromatase inhibitor when compared with tamoxifen [Hazard ratio (HR) = 1.09; 95% confidence interval (CI) = 0.96–1.23, p-value = 0.18]. The 5-year rate of osteoporotic fracture for patients treated with either an aromatase inhibitor or tamoxifen was 7.5% and 6.9%, respectively. A completed sensitivity analysis did observe a decreased risk of fracture associated with tamoxifen usage over time. Conclusion: We could not detect a significant difference in the rate of osteoporotic fracture among patients treated with an aromatase inhibitor versus tamoxifen. Nonetheless, the risk with tamoxifen was numerically lower and significantly decreased when accounting for total duration of endocrine therapy.
