The Food and Drug Administration has approved a new imaging agent to detect prostate cancer after it has spread to other parts of the body, the company that makes the agent said Thursday.
Experts say the tracer, made by medical imaging company Lantheus, will give doctors an important visual aid to guide them to metastatic prostate cancer cells that, before now, were difficult to spot.
Prostate cancer is the second leading cause of cancer deaths in men in the United States, after lung cancer, according to the American Cancer Society. More than 34,000 men die of the disease every year.
When prostate cancer spreads, it often goes into the bones, said Dr. Michael Morris, a medical oncologist at Memorial Sloan Kettering Cancer Center in New York City. That makes it difficult to detect using traditional imaging techniques.
"It's really hard to take pictures of what's going on inside of bone," Morris said, adding that traditional scans tend to find problems in the tissue surrounding bones, after damage has already been done.
"Now we don't have to wait for that," Morris said, who was involved with clinical trials of the tracer. "We can detect it much more clearly and much earlier than we could before."
The new technique uses a tracer molecule that seeks out a protein found on most prostate cancer cells called prostate-specific membrane antigen, or PSMA. The tracer, which is injected into the bloodstream, lights up those cells during a PET scan.
A similar tracing agent, which also seeks out PSMA, was approved by the FDA in December for use at two California hospitals: the University of California, Los Angeles and the University of California, San Francisco. The facilities had been researching this kind of technology since 2015.
"We've been using it for many years and it works great," said Dr. Thomas Hope, director of molecular therapy in UCSF's Department of Radiology and Biomedical Imaging. "We can actually see where the disease is and now people are getting targeted radiation."
"It's redefining how we think about prostate cancer," he said.
The new approval will be the first such tracer for advanced prostate cancer commercially available nationwide.
The scan isn't meant to replace PSA testing, a common prostate cancer screening tool. PSA stands for prostate-specific antigen, a protein found in the blood. Instead, it's meant for men who have already been diagnosed with the disease.
The scan would be most useful for prostate cancer patients who have rising PSA levels after they have undergone treatment, including surgery and radiation, said Dr. Xiao Wei, an oncologist at Dana-Farber Cancer Institute in Boston. A rising PSA level would indicate that the cancer has spread elsewhere in the body.
While Wei and other prostate cancer experts agreed that the imaging would give them more information about metastatic cancer, it remains unclear what they should do with the information.
"The huge looming question is, does it actually impact what we do for the patient? Will that help us improve outcomes?" said Dr. Justin Gregg, an assistant professor of urology and health disparities research at MD Anderson Cancer Center in Houston.
Prostate cancer treatment is often personalized, depending on a man's age, any other risk factors he might have or how aggressive the cells look under a microscope. Treatment, which can include radiation and removal of the prostate, can have significant side effects, including impotence and incontinence.
And not all metastatic prostate cancers will threaten a man's life.
"We may find deposits, but in an elderly man 75 or 85 years old, they might sit there and not require urgent treatment," said Dr. Derek Raghavan, president of the Levine Cancer Institute in Charlotte, North Carolina. "There is also a variant of prostate cancer that can be metastatic and actually not harm the patient for several years."
The new imaging is unable to determine which kinds of prostate cancer cells are likely to be more dangerous, Raghavan said.
"My guess is that as they develop the technology," he said, "they will develop a refined method for identifying those with a rapid growth potential."
This story was originally published on NBC News.