Patients with metastatic castration-resistant prostate cancer who underwent prior treatment with external beam radiation therapy (EBRT) and were treated with radium-223 (Ra-223) did not experience an increased relative incidence of hematological toxicity (blood-related side effects) when compared to patients who did not receive EBRT to the bone, recent study findings demonstrated.
Results from this study were presented during a poster session at the 2024 ASCO Genitourinary Cancers Symposium.
Researchers presented findings from the REASSURE study, which launched on Aug. 20, 2014, is estimated to be completed on February 28, 2025, and enrolled 1,474 patients, according to its listing on clinicaltrials.gov.
With a data cutoff of March 20, 2019, this evaluation of United States-based patients who were treated with EBRT within two years prior to receiving their first dose of Ra-223 (118 patients) as compared to the overall United States subset of REASSURE participants (498 patients) had a median duration of observation of 11.7 months for those treated with EBRT (median age 72) and 12 months for patients in the U.S.-based subset who did not receive EBRT to the bone (median age 75).
Drug-related hematological treatment-emergent side effects were proportionately similar between the EBRT cohort and the those who did not receive EBRT to the bone, occurring in 8.5% (10 of 118 patients) and 9.7% (37 of 380 patients), respectively, while severe or worse drug-related TEAEs occurred in 8.4% (10 of 118 patients) and 10.5% (40 of 380 patients), respectively. Treatment-emergent side effects resulted in Ra-223 discontinuation for five and 16 patients, respectively, and drug-related severe side effects resulted in death for one patient in each cohort.
Eight patients in the EBRT cohort (6.8%) and 11 patients who did not receive EBRT to the bone (2.9%) experienced bone fractures, while a combined six second primary malignancies (SPMs) were experienced by 4% of patients who had been treated with EBRT (five patients), five SPMs occurred among five patients (1%) who did not receive EBRT to the bone and a total of 11 SPMs occurred among 2% of overall subset (10 of 498 patients).
Previous findings from REASSURE, published in eClinicalMedicine, showed that at the data cutoff of March 20, 2019, and a median follow-up of 11.5 months, 1% (21 of 1,470 evaluable patients) had experienced 23 total SPMs, while during Ra-223 therapy 21% (311 of 1,465 evaluable patients) experienced treatment-emergent severe side effects and 35% (510 patients) had drug-related side effects. Six months following the completion of Ra-223 therapy, 15% of patients (214 patients) had experienced severe or life-threatening hematological toxicities, and 5% of patients (80 patients) had post-treatment, drug-related severe side effects. Seventy patients (5% of patients) experienced fractures.
“Ra-223 is a treatment for men with prostate cancer that doesn’t respond to regular hormone therapy and has spread to their bones,” researchers wrote in a poster presented as part of the ASCO GU symposium. “This treatment has been proven to help these men live longer and enhance their quality of life. EBRT is a highly effective treatment for easing bone pain in men with prostate cancer. We wanted to find out how safe it is for men to receive Ra-223 treatment after having EBRT.
“In the study, 118 men with prostate cancer received EBRT before getting Ra-223, and five men had EBRT at the same time as Ra-223. Patients who had EBRT to the bone before Ra-223 didn’t experience more blood-related issues than patients who didn’t receive EBRT. The overall occurrence of other cancers and fractures remained low, and there were no blood-related cancers.”
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