January 22, 2016
Have any cancer cells escaped the prostate? This is the question that every man who has prostate cancer, and every doctor treating him, wants to answer. Now there's a way to find out without making an incision or taking another biopsy sample. It's a brand new technique, called PSMA imaging, and it uses a PET (for positron emission tomography) scanner.
The technique was developed by Martin G. Pomper, M.D., Ph.D., the William R. Brody Professor of Radiology and Director of the Division of Nuclear Medicine and Molecular Imaging, and the original support to develop it came from a grant made by Patrick C. Walsh Prostate Cancer Research Fund. "This truly is individualized medicine, and we can really help patients with it," says Pomper; in fact, men with prostate cancer from around the world have flown to Johns Hopkins just to have this test done. "The results from this new radiotracer have changed how the disease is being managed in some patients. It, and others like it being used in Europe, have caught on like wildfire." At medical meetings devoted to prostate cancer, sessions are now being taught on PSMA imaging. Here's why this is such a breakthrough: Previously, doctors have only been able to see prostate cancer, either as a tumor or at metastatic sites, when there have been enough cancer cells gathered together to make a critical mass that would show up on MRI or another form of imaging. There was no way to target prostate cancer cells specifically. But what if there could be a way to make those cells light up somehow? With this in mind, Pomper figured out a way to engineer a harmless radioactive tracer that would attach itself specifically to prostate cancer cells. The tracer targets something on the surface of these cells: a molecule called PSMA, for (prostate-specific membrane antigen). "PSMA is a protein that is present in high concentrations on the surface of prostate cancer cells," Pomper says. "PET is a sensitive imaging technique that can allow us to see tumors deep within the body. PET works by detecting the radioactive molecules we made to 'tag' the prostate cancer cells specifically."
Previously in Discovery, we reported that Pomper had discovered and tested the first PSMA-targeting PET agent in a clinical trial. Now he has refined this — alphabet soup alert here — into a second-generation, PSMA-targeting PET agent called DCFPyL. Pomper is excited about the potential for DCFPyL to help men throughout the prostate cancer spectrum. "This agent has vastly higher sensitivity and specificity, and it provides sharper images," he says. "That will enable us to expand the use of imaging, not only to primary disease, but to see if the disease has returned after initial treatment, to help make treatment more accurate, and even as a monitoring tool for men on active surveillance. We believe that the images we are getting are the clearest ever obtained for prostate cancer in a human being." As a bonus, because PSMA is also expressed in the blood vessels of other types of cancers, this technique may also help spot other tumors, including certain forms of kidney cancer, he adds.
Pomper and colleagues recently published their results in Molecular Imaging and Biology.
Previously, doctors have only been able to see prostate cancer, either as a tumor or at metastatic sites, when there have been enough cancer cells gathered together to make a critical mass that would show up on MRI or another form of imaging. There was no way to target prostate cancer cells specifically.