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New imaging agent helps doctors hunt down metastatic prostate cancer

Dr. Jason Beland
This new advance is pushing science forward as researchers look for new ways to identify and treat metastatic cancer.

When prostate cancer metastasizes, doctors know that it most often will be found in bones, the lungs or the liver. But that doesn’t always mean it’s easy to find. Metastatic cancer cells often nest in different places in the body in numbers so small, or form tumors so tiny, they may not show up on some scans.

Recently, however, the U.S. Food and Drug Administration (FDA) approved a new imaging agent called piflufolastat F-18 (Pylarify®) to help make metastatic prostate cancer easier to find. The radioactive agent is designed to provide more complete information to doctors treating men diagnosed with recurrent or metastatic prostate cancer, giving them a clearer picture of whether their cancer has spread and where it may be found. It may also be used for some higher-risk patients with a primary prostate cancer diagnosis to see whether their cancer has already spread.

While the advance doesn’t directly affect health outcomes for men with prostate cancer, it is pushing science forward as researchers look for new ways to identify and treat the disease. It may also help doctors and patients make more informed decisions on treatment options.

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Prostate cancer facts

Prostate cancer is the second most common cancer diagnosed in the United States—behind breast cancer—and the most common cancer diagnosed in men.

More than 34,000 men in the United States die each year from prostate cancer, making it the second leading cause of cancer deaths in U.S. men. It’s also expected to be the leading cause of new cancer diagnoses in U.S. men this year, with 248,530 cases predicted, according to the National Cancer Institute.

Prostate cancer is highly treatable, especially when detected early. The five-year survival rate for men diagnosed with the disease is 97.5 percent. That rate drops to 30 percent when the cancer is diagnosed after it’s metastasized.

How radioactive agents work

Radioactive tracer drugs used to diagnose and treat cancer work by seeking out and attaching themselves to specific proteins on cancer cells and illuminating the cells during imaging scans. Piflufolastat F-18 is designed to latch onto prostate-specific membrane antigens (PSMAs found on prostate cancer cells, lighting them up during a PET/CT (positron emission tomography/computed tomography) scan. The drug is injected intravenously prior to a PET/CT procedure. The PET scan illuminates cancer cells, while the CT shows the anatomic configuration of the part of the body being scanned.

Scientists are just beginning to scratch the surface on the potential of these agents, known as radiopharmaceuticals, which use radioactive particles called radioisotopes either as cancer imaging agents, as targeted treatments, or both.

Piflufolastat F-18 is only the second drug available in the United States for imaging PSMA-positive lesions, but the first to be commercially available. The FDA approved Gallium 68 PSMA-11 in December for use at two California universities that developed that drug.

A study released in June on another radiopharmaceutical found that treatment with Lu-PSMA-617 increased the lifespan of men with metastatic castration-resistant prostate cancer by an average of four months. Lu-PSMA-617 uses the radioactive component lutetium-177. Its manufacturer  plans to submit the drug for FDA approval later this year.

Similar drugs have already been used extensively in Australia and several European countries.

“With conventional imaging, we’re waiting for the disease to look different or grow to a certain size before we think it’s abnormal,” says Jason Beland, MD, Medical Director of Imaging Services at Cancer Treatment Centers of America® (CTCA), Atlanta. “Now we can take the PET scan and the CT scan, and we overlay them. So, we’re seeing where things are, the lymph nodes and other things that may look normal on a regular CT scan, but now they’re lighting up. That’s telling us that there’s disease.”

Learn more about prostate cancer risk factors.

How are these drugs used in patients?

The FDA’s approval of piflufolastat F-18 covers its use in detecting prostate cancer in two types of patients:

  • Those with a primary diagnosis, who may experience positive outcomes with surgery or other therapy, but have a high risk for the cancer spreading to other parts of the body
  • Those whose cancer is suspected of having recurred based on elevated PSA (prostate-specific antigen) levels in their blood

“We need to understand how best to use this test and only employ it when it’s warranted, in these very specific situations,” Dr. Beland says. “We’re not talking about giving it to everyone who comes in off the street.”

The initial focus of piflufolastat F-18 PET scans is likely to be on patients with recurrent disease, says Sean Cavanaugh, MD, Chair of the CTCA® Department of Radiation Oncology.

There may be some concern that false readings indicating metastatic disease could lead some doctors to forego standard treatments, such as surgery or radiation therapy, that may potentially extend the life of patients who only have a primary tumor. The FDA acknowledges that “there is a risk of misdiagnosis because piflufolastat F-18 binding may occur in other types of cancer as well as certain non-malignant conditions, which may lead to image interpretation errors.”

Comparing testing options

Other tools being used to detect prostate cancer include CT scans (without the PET component), magnetic resonance imaging (MRI) scans and some nuclear medicine scans, such as bone scans. But unlike the PET scans using piflufolastat F-18, each of these imaging techniques is limited in its ability to detect prostate cancer lesions.

MRIs are better at characterizing localized disease, Dr. Cavanaugh says, while using Gleason and PSA scores are recommended for determining patients most at risk.

CT scans, which use a form of X-ray, and bone scans are regularly used to check for evidence of metastatic cancer. “Neither is particularly good at finding individual prostate cancer cells, and thus can miss very small tumors,” the National Cancer Institute says in a May 2020 article. “And bone scans can detect bone damage or abnormalities that were caused by something other than cancer (e.g., arthritis), resulting in ‘false-positive’ findings that can lead to unnecessary additional testing.”

As with other drugs, taking piflufolastat F-18 may cause some side effects. Typical adverse reactions include headaches, altered taste and fatigue.

Dr. Cavanaugh says it’s much too soon to know what impact piflufolastat F-18 will have when it comes to prostate cancer, because the radiopharmaceutical is just beginning to find its role.

“Fundamentally, the use of imaging in the management of prostate cancer is more subtle and complex than for some other cancers,” Dr. Cavanaugh says. “It is very rare for a new imaging technology to be used the same way at the time of approval versus 10 years later. Clinical utility grows organically with time and experience.”

Making informed decisions

Unfortunately, for some patients, detecting and locating metastatic prostate cancer cells may confirm a diagnosis for which there are few treatment options. It may, however, help doctors and patients make more informed decisions on how to move forward.

“Here we have a tool that can help us find stage 4 patients sooner, which might be able to spare some men therapy that will not benefit them,” Dr. Cavanaugh says. “Another thing it may do is disqualify some perceived oligometastatic patients [patients thought to have few metastatic tumors] from aggressive therapy by finding additional metastases and cementing their status as truly stage 4 palliative patients.”

Then again, a PET scan using piflufolastat F 18 that does not show the presence of metastatic cancer may make doctors more confident that a cancer recurrence—or a high-risk primary diagnosis—is indeed localized and proceed with treatment plans geared to that situation, Dr. Cavanaugh says.

“Ruling out distant disease at the time of diagnosis and, if needed, at the time of recurrence is the primary use of imaging in the management of prostate cancer,” he says.

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