Evaluating the combination of sipuleucel-T with radium-223 in men with metastatic castration-resistant prostate cancer spread to the bone.

The study investigated the effectiveness of combining sipuleucel-T (Provenge) with radium-223 (Xofigo) therapy in men with castration-resistant prostate cancer (CRPC) that has spread to the bones. The key finding was that the combination therapy improved the survival rates of these patients. 

Prostate cancer often grows in response to male sex hormones such as testosterone. Hormonal therapy can be given to these patients to reduce these hormones and therefore to stop the cancer from growing. Castrate-resistant prostate cancer (CRPC) has become resistant to hormone therapy. CRPC can spread to other organs such as the bones. Metastatic CRPC (mCRPC) is more difficult to treat. Other therapies are needed for these patients. 

Sipuleucel-T is a vaccine that takes immune cells from the patient that are modified into the lab to attack and kill cancer cells. It is approved for the treatment of mCRPC. Radium-223 is a drug that contains a radioactive substance that targets cancer in the bone. It then releases radiation directly to the cancer in the bone, without damaging healthy surrounding tissue. It is approved for the treatment of prostate cancer that has spread to the bones. Both drugs have shown good effectiveness on their own. However, the effectiveness of sipuleucel-T and radium-223 combined for the treatment of mCRPC that has spread to the bones is currently under investigation.

This study involved 32 patients with mCRPC. They were randomly assigned to 2 equal groups. Group 1 received sipuleucel-T and radium-223 and group 2 received sipuleucel-T alone. They were followed up for an average of 1.6 years. Patients were evaluated for immune responses and for tumor responses. Tumor response was evaluated through the PSA (prostate-specific antigen; a protein made by the prostate that increases in prostate cancer) blood levels.

After 6 weeks, the immune response in group 2 was 3.2 times higher than in group 1. However, significantly more patients in group 1 (33%) had a more than 50% reduction in PSA levels compared to group 2 (0%). Also, survival without cancer worsening was significantly longer in group 1 (39 weeks) compared to group 2 (12 weeks). Patients in group 1 were 68% more likely to not have cancer progression compared to group 2.

Side effects were the same as those already known for each drug. In group 1, nausea, diarrhea and low blood cell counts were more common.

The study concluded that the combination of sipuleucel-T and radium- 223 may improve survival in patients with CRPC that has spread to the bones.

This study had a very small number of participants and a short follow-up period. Larger studies are needed to confirm these findings. This study received support from the manufacturers of both sipuleucel-T and radium-223.