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Real-World Use of Bone Modifying Agents in Metastatic Castration-Sensitive Prostate Cancer.

BACKGROUND
Bone modifying agent (BMA) therapy is recommended for metastatic castration-resistant prostate cancer (mCRPC) but not metastatic castration-sensitive prostate cancer (mCSPC). BMA treatment in mCSPC may therefore constitute overuse.


METHODS
In this retrospective cohort study using linked Surveillance, Epidemiology, and End Results-Medicare data, we included patients diagnosed with stage IV prostate adenocarcinoma from 2007-2015, who were age ≥66 years at diagnosis and received androgen deprivation or antiandrogen therapy. We excluded patients who had previously received BMAs or had existing osteoporosis, osteopenia, hypercalcemia, or prior bone fracture. The primary outcome was receipt of BMA (zoledronic acid or denosumab) within 180 days of diagnosis (emergence of CRPC within this time frame is unlikely). Secondary outcome was BMA within 90 days. Exposures of interest included practice location (physician office vs. hospital outpatient) and specialty (medical oncologist vs. urologist) of treating physician.


RESULTS
Our sample included 2,627 patients, of which 52.9% were treated by medical oncologists and 47.1% by urologists; 77.7% and 22.3% received care in physician office and hospital outpatient locations, respectively. Overall, 23.6% received a BMA within 180 days; 18.4% did within 90 days. BMA therapy was more common among patients treated by oncologists (odds ratio = 8.23, 95% confidence interval = 6.41 to 10.57) and in physician office locations (odds ratio = 1.33, 95% confidence interval = 1.06 to 1.69). Utilization has increased: 17.3% of patients received BMAs from 2007-2009 (17.3% zoledronic acid, 0% denosumab), and 28.1% from 2012-2015 (8.4% zoledronic acid, 20.3% denosumab).


CONCLUSIONS
Among mCSPC patients who had no evidence of high osteoporotic fracture risk, over one-quarter received BMAs in recent years. This overuse may lead to excess costs and toxicity.