A Xofigo Update
Posted: 22 Jul 2015 06:46 PM PDT
BY MARK SCHOLZ, MD
Since Xofigo was FDA approved two years ago, the doctors at Prostate Oncology—Dr. Richard Lam, Dr. Jeffrey Turner and I—have been avid users. So this seems to be a good time to provide an informal update of our experience with Xofigo to the present time.
The clinical trial that led to Xofigo’s approval by the FDA was a prospective, placebo-controlled study demonstrating improved survival in Xofigo-treated men compared to men treated with placebo alone. The trial showed a very low incidence of side effects and good relief for men who were suffering from bone pain.
Xofigo is made out of radium, a radioactive element. After it is injected into the blood stream it concentrates near the cancer and delivers a potent dose of radiation. So after Xofigo is injected into the patient, it travels through the blood stream and concentrates in the irritated areas of the bone and emits radiation where the cancer is most active. Since prostate cancer spreads almost exclusively to bone, an injection of Xofigo ends up targeting most if not all of the cancer. Radiation consists of high energy, subatomic particles that blast cellular DNA. Once the DNA of the cancer cell has been hit, the cell is rendered incapable of reproduction. If you stop cancer reproduction you basically stop the cancer.
To almost everyone, radiation conjures up horrible visions of toxicity. Fortunately, bone marrow toxicity is rare in men because Xofigo emits a different type of radiation, “alpha particles,” rather than the standard “photon type” of external beam radiation. Alpha particles dissipate their energy over a very short distance, only a couple of millimeters. External beam radiation therapy, the type of radiation that has traditionally been relied on to kill cancer cells in the bone, needs to be used very judiciously because the radiation is “beamed” through the body to hit the target in the bone. Typically it causes irreversible damage to the surrounding bone marrow.
Over the last two years at Prostate Oncology, we have treated over 50 patients with Xofigo. The treatment has been very well tolerated. Occasionally, we have seen a few patients with mild diarrhea or nausea that has been easily managed with common medications. Men experiencing pain from cancer usually see either partial improvement or total resolution of their pain after one to three of the monthly treatments.
As reported from the original study that led to FDA approval, even though pain relief occurs and alkaline phosphatase (ALP) levels in the blood decline, PSA may continue to rise. This “disconnect” between PSA and other clinical parameters such as pain and ALP can be disconcerting to doctors and patients alike. The reason that it occurs is unclear. A similar phenomenon has been observed with another FDA-approved cancer therapy called Provenge.
Experts hypothesize that the survival advantage from Xofigo and Provenge is due to a slowing of cancer progression rather than an actual regression of the cancer. This “slowing” is powerful enough to extend patients’ lives but insufficiently powerful to consistently induce a decline in PSA. However, in our practice at Prostate Oncology notable declines in PSA have been observed in a few patients treated with Xofigo. One patient dropped his PSA from 50 down to zero and his PSA still remains at undetectable levels. Another recent patient has dropped his PSA from 150 down to 8.
For the patients on Xofigo who have rising PSA levels, it is logical to consider adding another effective anticancer agent such as Xtandi, Zytiga or Taxotere. It is encouraging to know that several studies now show that Xofigo can be safely combined with these other effective therapies.
Xofigo has been a very welcome addition to our anticancer armamentarium. The standard FDA approved protocol consists of a course of monthly treatments continued for a total of six months. Further trials are in progress to study the potential advantages of continuing Xofigo for longer than six months. Our experience to date suggests that longer therapy would indeed be advantageous in some instances.