Commenting on the ALSYMPCA follow-up study presented at the Genitourinary Cancers Symposium, Michael J. Morris, MD, a medical oncologist at Memorial Sloan Kettering Cancer Center, New York, said that radium-223 was a very effective and safe drug, but its actual target and mechanism of action are not well understood. He contrasted this drug with orteronel, a drug for which the mechanism of action is well understood but that did not extend survival in patients with hormone-refractory prostate cancer.

Dr. Morris said that there are several issues that remain to be resolved with radium-223: the optimal dose, the number of doses, how to combine and sequence radium-223 with other agents, identifying response biomarkers, and understanding the target.

Note of Caution

Maha H. Hussain, MD, FACP, FASCO, Professor of Medicine and Urology at the University of Michigan Comprehensive Cancer Center, Ann Arbor, said that the safety of radium 223 was reassuring. “One of the concerns with radiopharmaceuticals is long-term effects. The data from ­ALSYMPCA is  reassuring regarding the safety of radium-223 in terms of bone marrow function and leukemias. This drug is likely to move forward to earlier stages of the disease, where long-term side effects become even more important,” she said.

Nevertheless, Dr. Hussain sounded a note of caution: “Even though radium-223 appears to be safe to combine with other therapies and to use earlier in the course of disease, we still have to be careful in monitoring patients. For example, take the case of mitoxantrone, a drug that appeared to be safe in patients with metastatic castration-resistant prostate cancer, however, when tested  earlier in the course of disease, was associated with acute myelogenous leukemia.” ■

Disclosure: Dr. Hussain is the lead investigator for an upcoming trial of radium-223. Dr. Morris reported no potential conflicts of interest.