Radium-223 Safe and Effective to Treat Metastatic Castration-Resistant Prostate Cancer

Treatment with radium-223 was safe and effective in patients with metastatic castration-resistant prostate cancer and did not prevent them from receiving subsequent therapies such as chemotherapy, according to an analysis of the REASSURE study of patients treated in the United States.

Findings from the study, which were presented at the 2023 ASCO Annual Meeting, demonstrated that most patients completed five to six injections of radium-223 and no new safety signals were observed. In addition, treatment with radium-223 resulted in an overall survival (the time from treatment when a patient with cancer is still alive) of approximately 18 months in patients with metastatic castration-resistant prostate cancer.

“Our observations in this study show that radium-223 can be integrated into the treatment sequence for patients with (metastatic castration-resistant prostate cancer),” Dr. Daniel Y. Song, co-director of the prostate cancer multidisciplinary clinic and professor of radiation oncology and molecular radiation sciences at Johns Hopkins Sidney Kimmel Comprehensive Cancer Center in Baltimore, said during the poster presentation.

In this analysis, researchers focused on patients with confirmed metastatic castration-resistant prostate cancer from the U.S. who were scheduled to receive treatment with radium-223.

Radium-223 is a radioactive isotope that emits low levels of alpha particle radiation, according to the National Cancer Institute. It acts similarly to calcium by accumulating in areas of bone such as areas where metastases are forming. Since it emits very low levels of radiation, it limits damage to surrounding tissues.

Researchers primarily focused on short- and long-term safety including second primary malignancies and the incidence of bone marrow suppression (when fewer blood cells are made in marrow, which can cause anemia). In addition, researchers also monitored for patient-reported pain.

Researchers included 498 patients (median age, 74 years) in this analysis who were enrolled in the REASSURE study from 2014 to 2017.

In the analysis, 81% of patients had bone metastases only. Between five and six injections of radium-223 were received by 69% of patients.

Most patients — 77% — received at least one prior life-prolonging therapy such as Xtandi (enzalutamide; 48%), Zytiga (abiraterone; 45%), Jevtana (cabazitaxel; 6%), docetaxel (25%) or Provenge (sipuleucel-T; 24%).

Researchers noted that some patients in this analysis received concomitant Xtandi (enzalutamide; 31%) and concomitant bone health agents (47%). Thirty-one percent of patient received at least one life-prolonging therapy after treatment with radium-223.

Song noted that 37% of patients had received prior chemotherapy and 16% of patients who did not receive prior chemotherapy required either therapeutic or preventive treatments for bone marrow suppression.

More than half of the patients (58%) in this analysis who reported pain at the start of the study experienced a clinically meaningful pain response during treatment.

Any-grade drug-related treatment-emergent side effects occurred in 32% of patients, whereas side effects considered severe or worse were observed in 10% of patients. Four percent of patients discontinued treatment with radium-223 as a result of drug-related treatment-emergent side effects.

Treatment-emergent serious side effects occurred in 21% of patients, and drug-related serious side effects were observed in 6% of patients. The most common any-grade drug-related treatment-emergent side effects, which occurred in 5% or more patients, were fatigue (9%), diarrhea (10%), nausea (7%) and anemia (8%). Song noted in the presentation that these “were side effects which were known and previously established to be an inherent risk for radium-223.”

Four percent of patients had fractures and 2% developed bone disorders. Eleven second primary malignancies were observed in 10 patients (2%).

During follow-up, 60% of patients died, and the median overall survival was 17.8 months. Song said that the overall survival in the REASSURE study compares favorably with the ALSYMPCA trial results, which were 14.9 months.

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