By Charlie Schmidt
Two early warning signs of possible prostate cancer are a high level of prostate-specific antigen (PSA) in the bloodstream and an abnormal digital rectal exam. When either occurs, a prostate biopsy is usually done to see if that warning sign is being caused by prostate cancer. A new study indicates that images from an MRI scan can help improve biopsy results.
A standard biopsy is done like this: A doctor inserts an ultrasound probe into a man’s rectum. The probe uses high-frequency sound waves to create images of the prostate gland. These images help the doctor guide several small, hollow needles into the gland. These needles grab samples of prostate tissue that are later analyzed to determine if prostate cancer cells are present.
One drawback with this method is that ultrasound can’t readily distinguish cancerous tissue from healthy tissue. That means the needles could miss a section of prostate tissue harboring potentially aggressive cancer cells. In fact, ultrasound-guided biopsies miss such high-grade tumors about 40% of the time.
A study in The Journal of the American Medical Association reports promising results from a more targeted way to biopsy the prostate. Researchers call it “fusion-guided biopsy” because it fuses ultrasound images with high-resolution pictures of the prostate made by a newer technology called multi-parametric magnetic resonance imaging (MP-MRI). Prostate tumors show up on MP-MRI as dark spots. By adding MP-MRI images taken beforehand to the real-time ultrasound images, doctors can target suspicious regions of the gland while steering clear of healthy tissue.
Earlier trials suggested that doing fusion-guided biopsy and standard biopsy together is better at detecting potentially harmful tumors than standard biopsy alone.
The JAMA study set out to compare the two approaches independently. Mohammad Minhaj Siddiqui, an assistant professor of urologic surgery at the University of Maryland, and his colleagues recruited 1,003 men with either a high PSA level or an abnormal digital rectal exam and at least one suspicious spot identified by MP-MRI. All the men had two biopsies during a single session: a fusion-guided biopsy by one doctor, followed by a standard biopsy by a different doctor who wasn’t shown the MP-MRI images.
Prostate cancer diagnoses were almost identical in both methods: fusion-guided biopsy detected 461 cases, compared with 469 cases detected by the standard biopsy. However, fusion-guided biopsy detected 30% more high-grade cancers, which are potentially more dangerous, and 17% fewer slow-growing, low-risk cancers than standard biopsy.
“The fusion-guided method allowed us to reliably find more high-grade prostate tumors,” said Siddiqui, who did the study while he was a fellow at the National Institutes of Health. “And it also reduced the diagnoses of indolent tumors that aren’t likely to harm the patient.”
The combination of fusion-guided and standard biopsies detected an extra 103 cancers, or 22% more than either method alone. But the vast majority of these additional cancers were slow-growing, low-risk tumors. “This suggests that fusion-guided biopsy by itself is sufficient,” Siddiqui said. “Combining the two biopsies likely exposes the patient to more discomfort and even a higher risk of complications such as infection and bleeding, with limited clinical benefit.”
In an accompanying editorial, Lawrence H. Schwartz, of the Columbia University College of Physicians and Surgeons, and Ethan Basch, a medical oncologist at the University of North Carolina and an associate editor of JAMA, wrote that fusion-guided biopsy promises “more appropriate treatment recommendations, such as higher-intensity treatment for high-risk disease and active surveillance for men with low-grade tumors.”
Yet Schwartz and Basch emphasize that additional studies are needed to determine whether the fusion-guided biopsy has any influence on long-term survival, a point with which Siddiqui agrees.
Marc Garnick, the Gorman Brothers Professor of Medicine at Harvard Medical School and Beth Israel Deaconess Medical Center and Editor in Chief of HarvardProstateKnowledge.org, said results from the study suggest that fusion-guided biopsy — along with newer molecular tools for characterizing prostate cancer — could help patients make more rational treatment choices. But he emphasized that data about the final outcomes of patients who undergo fusion-guided biopsy are desperately needed. “We need to know if these diagnostic aids will lead to both short-term and long-term clinical benefits,” he said.