Endocrine therapy improves survival outcomes in women with oestrogen-receptor-positive (ER-positive) breast cancer by reducing oestradiol serum concentration or action. Oestradiol depletion predisposes to bone loss which might be further accelerated by coexisting conditions known to cause bone loss. The aim of this study was to determine the prevalence of secondary causes of bone loss in women receiving adjuvant endocrine therapy for ER-positive early (non-metastatic) breast cancer.
A retrospective study was conducted of all women with ER-positive early breast cancer who attended the Austin Hospital Breast Oncology Clinic between June 2014-2016. Women were excluded if they declined endocrine therapy. Secondary causes of bone loss were identified using clinical, biochemical and radiological data obtained from electronic medical records. Descriptive analysis was performed using SPSS version 23.0.
Seven hundred and forty-six women were included in the final analysis. At breast cancer diagnosis, 63.8% were postmenopausal (mean age 65.5±9.0 years) and 36.2% were pre- or perimenopausal (mean age 44.9±6.7 years). 36.3% of women had at least one secondary cause of bone loss identified. Clinical risk factors included current smoking (8.7%), family history of osteoporosis (7.2%), prolonged glucocorticoid exposure (3.8%), premature menopause prior to breast cancer diagnosis (2.7%), excessive alcohol intake (1.6%) and gastrointestinal malabsorptive disorders (1.5%). Biochemical factors included baseline vitamin D <50nmol/L (27.7%), history or current biochemical evidence of hyperthyroidism (22.0%), and primary hyperparathyroidism (7.3%).
At least 1 in 3 women had an additional secondary cause for bone loss identified. The majority of these factors are amenable to treatment or intervention. In this population of women susceptible to endocrine-therapy related bone loss, appropriate identification and early management may improve bone health. Larger controlled prospective studies are needed to evaluate whether correction of such secondary causes mitigates the accelerated bone loss and increased fracture risk in these women.