The novel radiopharmaceutical radium-223 (Xofigo) appears to have long term safety with minimal adverse events.

In an updated report, given at ASCO GU, on the ALSYMPCA trial of radium-233 (Xofigo), the researchers have found that there is no major safety issues identified within ~1.5 years after the completion of treatment in a population of men with metastatic castration-resistant prostate cancer (mCRPC) with bone metastases.

Xofigo, which has been approved in both the US and the European Union, it extended survival and addressed an “important unmet need,” according to researchers who initially reported the results of the phase III trial that led to the product’s approval.

According to the ASCO presentation, “We found that it has a very benign safety profile, and that was shown in the earlier phase I and phase II trials,” said lead author Sten Nilsson, MD, PhD, professor of oncology at the Karolinska Hospital, Stockholm, Sweden. “Now it is important that we try to follow the patients, and to see if any adverse events have developed and can be considered treatment related.”

It was disclosed that they have been following both hematologic and nonhematologic side effects, as well as the possible induction of secondary malignancies.

Thus far, they have not seen any cases of myelogenous leukemia, myelodysplastic syndrome, or primary bone cancer, he continued. “We feel that it is important to follow up on adverse events, and so far, Radium-223 has a very benign profile.”

Despite the poor prognosis for this disease radium-223 did extend survival. “The median survival was less than 1 year in placebo and 14.9 months in the active treatment arm, so the survival benefit was 3.6 months,” Dr. Nilsson said. “That is a very robust finding.”

He indicated that they will continue to follow the surviving patients, and updated study results will be presented in the spring, at the annual meeting of the American Society of Clinical Oncology.

Michael J. Morris, MD, a medical oncologist from Memorial Sloan-Kettering Cancer Center, who was a discussant for the paper at ASCO said, “For those concerned about long term bone marrow toxicity, it looks like one can rest easy and there are no surprises coming down the pipe….. It prolongs survival and with a side effect profile that is tantalizingly close to zero.”

He did say that now that 1.5 years have passed since its approval, it is time to delve more deeply into finding out how the drug works, as much remains unclear. He said that it does seem that “one can go much higher on the dose and still not risk toxicity…… We don’t know how to leverage the gains with this drug as monotherapy into combinations with other treatments.”

He also said, “We also don’t know how to identify a responder or progresser on this drug.”

From: 2014 Genitourinary Cancers Symposium (GUCS): Abstract 9. Presented January 30, 2014.

Joel T Nowak, M.A., M.S.W.