A real-world evaluation of radium-223 in combination with abiraterone or enzalutamide for the treatment of metastatic castration-resistant prostate cancer

Safety and effectiveness of the radium-223-taxane treatment sequence in patients with metastatic castration-resistant prostate cancer in a global observational study (REASSURE)

BACKGROUND

Radium-223 and taxane chemotherapy each improve survival of patients with metastatic castration-resistant prostate cancer (mCRPC). Whether the radium-223-taxane sequence could extend survival without cumulative toxicity was explored.

METHODS

The global, prospective, observational REASSURE study (NCT02141438) assessed real-world safety and effectiveness of radium-223 in patients with mCRPC. Using data from the prespecified second interim analysis (data cutoff, March 20, 2019), hematologic events and overall survival (OS) were evaluated in patients who were chemotherapy-naive at radium-223 initiation and subsequently received taxane chemotherapy starting ≤90 days ("immediate") or >90 days ("delayed") after the last radium-223 dose.

RESULTS

Following radium-223 therapy, 182 patients received docetaxel (172 [95%]) and/or cabazitaxel (44 [24%]); 34 patients (19%) received both. Seventy-three patients (40%) received immediate chemotherapy and 109 patients (60%) received delayed chemotherapy. Median time from last radium-223 dose to first taxane cycle was 3.6 months (range, 0.3-28.4). Median duration of first taxane was 3.7 months (range, 0-22.0). Fourteen patients (10 in the immediate and four in the delayed subgroup) had grade 3/4 hematologic events during taxane chemotherapy, including neutropenia in two patients in the delayed subgroup and thrombocytopenia in one patient in each subgroup. Median OS was 24.3 months from radium-223 initiation and 11.8 months from start of taxane therapy.

CONCLUSIONS

In real-world clinical practice settings, a heterogeneous population of patients who received sequential radium-223-taxane therapy had a low incidence of hematologic events, with a median survival of 1 year from taxane initiation. Thus, taxane chemotherapy is a feasible option for those who progress after radium-223.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov identifier NCT02141438.

PLAIN LANGUAGE SUMMARY

Radium-223 and chemotherapy are treatment options for metastatic prostate cancer, which increase survival but may affect production of blood cells as a side effect. We wanted to know what would happen if patients received chemotherapy after radium-223. Among the 182 men treated with radium-223 who went on to receive chemotherapy, only two men had severe side effects affecting white blood cell production (neutropenia) during chemotherapy. On average, the 182 men lived for 2 years after starting radium-223 and 1 year after starting chemotherapy. In conclusion, patients may benefit from chemotherapy after radium-223 treatment without increasing the risk of side effects.

The safety of radium-223 combined with new-generation hormonal agents in bone metastatic castration-resistant prostate cancer: a systematic review and network meta-analysis

Patients with bone metastatic castration-resistant prostate cancer (mCRPC) might benefit from radium-223 (223Ra) combined with new-generation hormonal agents (NHAs) in terms of survival and quality of life (QoL). However, the safety of combination therapies remains unclear. Therefore, we aimed to perform a network meta-analysis by reviewing the literature about the combination of 223Ra with abiraterone acetate plus prednisone (AAP) or enzalutamide and to evaluate the safety of combination therapy in bone mCRPC patients. Ultimately, ten studies (2835 patients) were selected, including four randomized controlled trials (RCTs), five retrospective cohort studies, and one single-arm study. Overall, there was no difference in the incidence of fracture between the 223Ra+NHA combination group and the 223Ra monotherapy group (odds ratio [OR]: 1.46, 95% confidence interval [CI]: 0.91-2.34, P = 0.66), but the incidences in both the 223Ra+NHA combination group (OR: 3.22, 95% CI: 2.24-4.63, P < 0.01) and the 223Ra monotherapy group (OR: 2.24, 95% CI: 1.23-4.08, P < 0.01) were higher than that in the NHA monotherapy group. However, in the meta-analysis involving only RCTs, there was no difference between the 223Ra monotherapy group and the NHA monotherapy group (OR: 1.14, 95% CI: 0.22-5.95, P = 0.88), while the difference between the 223Ra+NHA combination group and the NHA monotherapy group remained significant (OR: 3.22, 95% CI: 2.24-4.63, P < 0.01). Symptomatic skeletal events (SSEs), SSE-free survival (SSE-FS), all grades of common adverse events (AEs), and ≥grade 3 AEs among all groups did not show any significant difference. Our results indicate that the combination of 223Ra with NHAs was well tolerated in bone mCRPC patients compared to 223Ra monotherapy, even though the incidence of fracture was higher in patients who received 223Ra than that among those who received NHA monotherapy. More evidence is needed to explore the safety and efficiency of 223Ra combination therapies.

Real-world effectiveness, long-term safety and treatment pathway integration of radium-223 therapy in patients with metastatic castration-resistant prostate cancer

Radium-223 dichloride (223Ra) is an α-emitter approved for the treatment of metastatic castration-resistant prostate cancer (mCRPC) with bone metastases, but without visceral involvement. Despite being a life-prolonging therapy (LPT), 223Ra remains underutilized. A large body of real-world evidence (RWE) for 223Ra has been published in the decade since the pivotal phase 3 ALSYMPCA study, a period during which the treatment landscape has continued to evolve. How to optimize 223Ra use, including how to integrate it into the mCRPC management pathway amongst other current LPTs (i.e., with respect to timing and concurrent, layered, or sequential use), is therefore of considerable interest. RWE studies lack the conventional restraints of clinical trials and can therefore help to build an understanding of how treatments may be best used in routine practice. Here we review RWE studies investigating the efficacy and safety of 223Ra in mCRPC [including in sequence with the recently approved 177-Lutetium conjugated to the ligand prostate-specific membrane antigen (177Lu-PSMA)], as well as response marker development, imaging techniques, and current clinical practice recommendations.

Second generation androgen receptor antagonists and challenges in prostate cancer treatment

Prostate cancer is a hormone-dependent malignancy, whose onset and progression are closely related to the activity of the androgen receptor (AR) signaling pathway. Due to this critical role of AR signaling in driving prostate cancer, therapy targeting the AR pathway has been the mainstay strategy for metastatic prostate cancer treatment. The utility of these agents has expanded with the emergence of second-generation AR antagonists, which began with the approval of enzalutamide in 2012 by the United States Food and Drug Administration (FDA). Together with apalutamide and darolutamide, which were approved in 2018 and 2019, respectively, these agents have improved the survival of patients with prostate cancer, with applications for both androgen-dependent and castration-resistant disease. While patients receiving these drugs receive a benefit in the form of prolonged survival, they are not cured and ultimately progress to lethal neuroendocrine prostate cancer (NEPC). Here we summarize the current state of AR antagonist development and highlight the emerging challenges of their clinical application and the potential resistance mechanisms, which might be addressed by combination therapies or the development of novel AR-targeted therapies.