Eric Johnson and Sumati Gupta are Oncologists, and Katerina Butler is a Clinical Oncology Pharmacist; all at George E. Wahlen Department of Veterans Affairs Medical Center in Salt Lake City, Utah. Eric Johnson is a Clinical Fellow and Sumati Gupta is an Assistant Professor, both at Huntsman Cancer Institute at the University of Utah in Salt Lake City. Correspondence: Eric Johnson (eric.johnson@hci.utah.edu)
Author disclosures The authors report no actual or potential conflicts of interest with regard to this article.
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Denosumab was also studied in the setting of nonmetastatic CRPC in the Denosumab 147 trial. The study enrolled 1432 patients and found a significantly increased bone metastasis-free survival by a median of 4.2 months over placebo (HR, 0.85; 95% CI, 0.73-0.98; P= .03). Denosumab significantly delayed time to first bone metastasis (HR, 0.84; 95% CI, 0.71-0.98; P= .03). OS was similar between groups (HR, 1.01; 95% CI, 0.85-1.20; P= .91). Rates of AEs and serious AEs were similar between groups, except for ONJ and hypocalcemia. The rates of ONJ for denosumab were 1%, 3%, 4% in years 1,2, 3, respectively; overall, < 5% (n = 33). Hypocalcemia occurred in < 2% (n = 12) in denosumab-treated patients. The authors concluded that in men with CRPC, denosumab significantly prolonged bone metastasis–free survival and delayed time-to-bone metastasis.37 These 2 studies suggest a role of receptor-activated nuclear factor κ-B ligand inhibitor denosumab in patients with nonmetastatic CRPC in the appropriate setting. There were delays in bony metastatic disease, but no difference in OS. Rare denosumab treatment–related specific AEs were noted. Hence, denosumab is not recommended for use in this setting.
Metastatic CRPC
Castration resistance typically occurs 2 to 3 years following initiation of ADT and the most common extranodal site of disease is within the bone in metastatic PC. Disease progression within bones after ADT can be challenging given both the nature of progressive cancer with osteoblastic metastatic lesions and the prolonged effects of ADT on unaffected bone. The Zometa 039 study compared ZA with placebo and found a significant difference in SREs (38% and 49%, respectively; P .03). No survival benefit was observed with the addition of ZA. Use of other bisphosphonates pamidronate and clodronate did not have a similar degree of benefit.38,39
A phase 3 study of 1904 patients found that denosumab was superior to ZA in delaying the time to first on-study SRE (HR, 0.82; 95% CI, 0.71-0.95) and reducing rates of multiple SREs (HR, 0.82; 95% CI, 0.71-0.94).40 This was later confirmed with an additional study that demonstrated treatment with denosumab significantly reduced the risk of developing a first symptomatic SRE, defined as a pathologic fracture, spinal cord compression, necessity for radiation, or surgery (HR, 0.78; 95% CI, 0.66-0.93; P = .005) and first and subsequent symptomatic SREs (rate ratio, 0.78; 95% CI, 0.65-0.92; P = .004) compared with ZA.28 These findings suggest a continued role of denosumab in the treatment of advanced metastatic CRPC from both control of bone disease as well as quality of life and palliation of cancer-related symptoms.
Radium-223 dichloride (radium-223) is an α-emitting radionuclide for treatment of metastatic CRPC with bone metastasis, but otherwise no additional metastatic sites. Radium-223 is a calcium-mimetic that preferentially accumulates into areas of high-bone turnover, such as where bone metastases tend to occur. Radium-223 induces apoptosis of tumor cells through double-stranded DNA breaks. Studies have shown radium-223 to prolong OS and time-to-first symptomatic SRE.41 The ERA-223 trial showed that when radium-223 was combined with abiraterone acetate, there was an increase in fragility fracture risk compared with placebo combined with abiraterone. Data from the study revealed that the median symptomatic SRE-free survival was 22.3 months (95% CI, 20.4-24.8) in the radium-223 group and 26.0 months (21.8-28.3) in the placebo group. Concurrent treatment with abiraterone acetate plus prednisone or prednisolone and radium-223 was associated with increased fracture risk. Osteoporotic fractures were the most common type of fracture in the radium-223 group and of all fracture types, differed the most between the study groups.42
Conclusions
Convincing evidence supports the ongoing use of bisphosphonates and denosumab in patients with osteoporosis, significant osteopenia with risk factors, and in patients with CRPC with bone metastasis. Bone metastases can cause considerable morbidity and mortality among men with advanced PC. Pain, fracture, and neurologic injury can occur with metastatic bone lesions as well as with ADT-related bone loss. Prevention of SREs in patients with PC is a reasonable goal in PC survivors while being mindful of managing the risks of these therapies.
