Treatments for prostate cancer are always evolving, and now research is pointing to new ways of treating a cancer that has just begun to spread, or metastasize, after initial surgery or radiation. Doctors usually give hormonal therapies in these cases to block testosterone, which is a hormone that makes the cancer grow faster. But newer evidence shows that treating the metastatic tumors directly with radiation can produce better results.
In March, researchers published the latest study that supports this approach. Based at Johns Hopkins University School of Medicine in Baltimore, the team used a method for delivering powerful beams of high-dose radiation to very small cancers in the body. This approach is called stereotactic ablative radiotherapy (SABR), and it can spare healthy tissues with remarkable precision. Doctors map out where to pinpoint the radiation in advance by putting patients into a computed tomography (CT) scanner that takes x-rays of the body from many different angles.
During their study, the Johns Hopkins team recruited 54 men with three or fewer metastatic tumors. All the men had already undergone initial treatment for cancer while it was still in the prostate, and some had also been treated with hormonal therapy, though not within six months of being enrolled for the research. The men were 68 years old on average, and they were each randomly assigned to one of two groups: A third of the men were placed in an observation (control) group, meaning they received no additional treatment until the study was over. The rest were given SABR at a rate of one to five treatments per tumor over a period of about a week.
Then the men were followed for six months and monitored for changes such as PSA increases, tumor growth, worsening symptoms, or how many men wound up on hormonal therapy.
Results showed that the SABR-treated men fared better in all respects. Overall, 19% of those who got the targeted radiation had their cancers progress, compared to 61% of men in the control group. Taken together, the findings support a view that all detectable lesions should be removed, if feasible, to maximize the odds “of a cancer cure,” according to the authors of an editorial accompanying the published paper.
What makes SABR effective for treating early-stage metastases? Scientists are trying to find out. The investigators behind this study speculated that irradiating visible traces of cancer might block signals that feed the growth of even smaller tumors that are still too small to see. It’s also possible that radiation induces a sort of vaccinating effect, which prompts the immune system to attack other tumor cells.
Meanwhile, SABR could soon benefit from an ability to flag even smaller tumors for treatment. A new type of imaging scan called PMSA-targeted positron emissions tomography (PET) was tested in the study, and it found very small tumors that CT scanning had missed.
Dr. Marc Garnick, Gorman Brothers Professor of Medicine at Harvard Medical School and Beth Israel Deaconess Medical Center, and editor in chief of HarvardProstateKnowledge.org, says the whole concept of treating metastatic prostate cancer “is undergoing re-evaluation.” He added, “The findings in this case need to be supported with a larger study. However, this research provides more evidence that for patients with less extensive metastasis, SABR treatments can significantly delay systemic therapies such as chemotherapy or hormonal treatment.”
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