Efficacy and toxicity of extending bone modifying agents beyond two years for bone metastases in breast or castrate-resistant prostate cancer patients: A systematic review.

Abstract

e24083 Background: Randomized clinical trials evaluated bone modifying agents (BMAs) such as bisphosphonates and denosumab for bone metastases for 1-2 years in duration even though BMA therapy is commonly administered for much longer. A systematic review on the risk-benefit of continuing BMAs for longer than 2 years in breast cancer or castrate-resistant prostate cancer was conducted. Methods: Medline, Embase and Cochrane Register of Controlled Trials were searched (1970 - February 2019) for randomized studies, observational studies, and case series reporting on BMA efficacy and toxicity beyond 2 years. Efficacy was assessed by skeletal-related event (SRE) rates and quality of life metrics. Toxicity was assessed by rates of osteonecrosis of the jaw (ONJ), renal impairment, hypocalcemia, and atypical femoral fractures (AFF). Results: Of 2107 citations, 64 studies were identified. A total of 3 prospective and 9 retrospective studies were eligible. Data beyond 2 years was limited to subgroup analyses in all studies. Three studies [zoledronate (ZOL) (n = 481), pamidronate (PAM) (n = 87), PAM-ZOL (n = 43) ibandronate (n = 30)] reported on SRE-related endpoints. Only one study reported SRE rates based on duration of BMA exposure and showed reduced SRE rates from 27.6% (0-24 months) to 15.5% ( > 24 months) over time. None reported on quality of life. All 12 studies [denosumab (n = 948), ZOL (n = 1036), PAM (n = 163), PAM-ZOL (n = 522), ibandronate (n = 118)] reported on at least one toxicity outcome. Data from 7 bisphosphonate studies (n = 1077) and 1 denosumab study (n = 948) reported on ONJ incidence. In 3 studies (n = 67, n = 221, n = 948), ONJ incidence ranged from 1-4% in the first 2 years and from 3.8-18% beyond 2 years. In another study (n = 252), the cumulative hazard of ONJ was 0% (1% ZOL), 3% (7% ZOL), 7% (21% ZOL) and 11% (21% ZOL) at 12, 24, 36, and 48 months, respectively (p = 0.005); 4 remaining studies reported 1 (n = 181), 3 (n = 57), 7 (n = 99) and 2 (n = 200) cases of ONJ, all after 24 months. Incidence of clinically significant hypocalcemia ranged from 1-2%. Incidence of severe renal function decline was ≤ 3%. AFF occurred in two subjects in one of two studies after 37 and 79 months of BMA exposure. Conclusions: Although the evidence informing the use of BMA is heterogeneous and based on retrospective analysis, BMA exposure beyond 2 years is associated with reduced SRE risk and increased ONJ incidence. Prospective randomized studies addressing the use of BMA for more than 2 years is needed with greater emphasis on quality of life.