Richard G. Stock, MD
The manageable safety profile of radium-223 dichloride (Xofigo) compared with other radiopharmaceuticals is appealing to oncologists treating castration-resistant prostate cancer (CRPC) that is metastatic to the bone, says Richard G. Stock, MD.
, Stock discusses the ideal patient for radium-223, its proper sequencing with mCRPC, and the future outlook for the therapy.
OncLive: What is the optimal use of radium-223?
: Obviously, it has been shown to improve survival in patients who have both CRPC and progressive disease on hormonal therapy with multiple bone metastases. The optimal use is in a patient with metastatic disease that primarily has bone metastases and, most often, radium-223 has been used later on after other first-line therapies. I see an opportunity for it to be used earlier during the course of mCRPC.
What is the mechanism of action for radium-223 and how does that compare with other agents in this space?
Radium-223 is radioactive and it has taken up sites of new bone formation. Where prostate cancer has metastasized to the bone is where you have very active bone formation, with bone being laid down by the body. It preferentially absorbs radium-223 and attacks the bone metastasis.
This is opposed to external-beam radiation, where you are basically delivering a photon and depositing energy into the site of the disease. Radium-223 is actually picking up the radioactive material, which is similar to other bone-forming elements, and going directly to the area of bone metastasis.
Where do you see radium-223 falling in terms of sequencing in mCRPC?
My experience has typically been to use radium-223 in patients who have failed other treatments, including the new androgen-targeted therapies, traditional hormonal therapies, and chemotherapy. Patients I tend to see in my practice have already received and failed on some of those treatments; they are receiving radium-223 because it is kind of the next in line in terms of treatment.
Do you think radium-223 will ever be used in an earlier setting?
There are some trials looking at moving it up that will hopefully come out and show that it has an improved efficacy earlier on in some patients.
How has the field of radiopharmaceuticals evolved over the years?
Many of the radiopharmaceuticals that have been previously used have targeted bone metastasis and they were actually very good at reducing it. The problem has been that they are very suppressive on the bone marrow. Radium-223 did not have these issues.
What else is on the horizon for radium-223?
It has become a mainline treatment, along with a bunch of other treatments in mCRPC. It has kind of fallen in line along with immunotherapy and androgen receptor–targeted therapy, and it has just opened up a whole new field for treating patients with mCRPC.
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