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Patients with metastatic, castration-resistant prostate cancer saw significant benefits from the combination of Xofigo and Xtandi.
For patients with metastatic, castration-resistant prostate cancer (mCRPC) and predominant bone metastases, treatment with Xofigo (Radium-223) plus Xtandi (enzalutamide) was associated with significant improvements in radiological progression-free survival (rPFS; the time a patient lives without their disease spreading or worsening) and overall survival (the time a patient lives, regardless of their disease status).
The findings were presented as part of data from the phase 3 PEACE-3 trial at the 2024 ESMO Annual Congress, with it also being noted that a bone-protecting agent will be mandatory if the combination is used.
“These results support the combination of [Xtandi] plus [Xofigo], plus a bone protecting agent, as a potential new first line mCRPC treatment option for patients with prostate cancer and bone metastases who have not received a prior androgen-receptor pathway inhibitor,” Dr. Silke Gillessen, a medical oncologist at Università della Svizzera italiana in Lugano, Switzerland, said in a presentation of findings.
There was a statistically significant improvement seen regarding the primary endpoint of rPFS in patients who received Xofigo plus Xtandi (222 patients) versus Xtandi alone (224 patients). The median rPFS was 19.4 months in the doublet arm compared with 16.4 months in the monotherapy arm. The 24-month rPFS rates were 45% versus 36%, respectively. Gillessen noted that the treatment effect on rPFS with the doublet versus monotherapy was consistent across all subgroups analyzed.
Further, at the interim analysis with 80% of OS events having occurred, the median OS was 42.3 months in the Xofigo plus Xtandi arm versus 35 months in the Xtandi arm.
Patients received Xtandi once daily in both groups, and those in the combination arm also received Xofigo intravenously every four weeks for six cycles.
Patients experienced a significant improvement in time to next treatment (TTNT) when they received Xofigo plus Xtandi versus Xtandi alone. At 24 months, the estimated proportion of patients who started the next systemic treatment was 29.9% in the doublet arm versus 50.9% in the monotherapy arm.
Data from the safety population of the Xofigo plus Xtandi arm (218 patients) versus Xtandi monotherapy arm (224 patients) revealed that 84% of patients versus 71% of patients experienced drug-related side effects, respectively. Patients in the combination arm versus monotherapy arm experienced serious side effects (43% versus 30%), serious drug-related side effects (8% versus 1%), grade 3 (severe) to 5 (fatal) side effects (66% versus 56%), and grade 3 to 5 drug-related side effects (28% versus 19%), respectively.
Seven patients in the combination arm died due to a side effect compared with four patients in the monotherapy arm; notably, no deaths were a result of drug-related side effects.
Additionally, treatment discontinuation rates due to toxicity were 11% in the doublet arm compared with 7% in the monotherapy arm. The most common grade 3 to 5 treatment-emergent side effects that occurred were hypertension (high blood pressure; 33.5% versus 34.4%), fatigue (5.5% versus 1.8%), fracture (5.1% versus 1.3%), anemia (low red blood cell count, 4.6% versus 2.2%), neutropenia (low count of neutrophils, a type of white blood cell, 4.6% versus 0%), bone pain (4.1% versus 4.9%), decreased weight (3.2% versus 0.4%) and spinal cord compression (2.8% versus 3.6%). Treatment-related side effects included hypertension (11.5% versus 12.1%), fatigue (4.1% versus 1.3%), anemia (2.8% versus 0%) and neutropenia (3.2% versus 0%), respectively.
“In general, before using this combination fully in our patients, I believe we need more data,” Dr. Karim Fizazi, a medical oncologist at Institute Gustave Roussy in Villejuif, France, said in discussion of the study findings. Fizazi noted that data from more phase 3 trials evaluating Xofigo are currently maturing.
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