Mayo Prostate Scan Catches Recurring Cancers Early

Wednesday, 13 Mar 2013 07:50 AM

 

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Mike Hawker travels 3,200 miles from his home in Anchorage to the Mayo Clinic every six months to get a test for microscopic signs that a rare form of prostate cancer he beat three years ago may have returned.
 
For Hawker, a Republican state representative in Alaska, the trips are a matter of life and death. About 200,000 men who had been treated for prostate cancer learn each year, sometimes too late, that their malignancies have returned. The Mayo Clinic test offers the promise of catching recurring tumors early, before they can kill.
 
Mayo’s medical center in Rochester, Minnesota, is the only facility in the Western Hemisphere to offer the 20-minute scan, enhanced by an injected radioactive drug that lets doctors see rapidly dividing cancer cells. Demand is surging, though scans are limited to eight patients a day, three days a week.

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Hawker, who survived an aggressive form of prostate cancer in 2010 that invaded everything from his knees to his eye sockets, sees the twice-yearly visits as his best hope.
 
“No one can figure out quite why I am alive,” said Hawker in an interview. “That machine is one of the diagnostic tools that is keeping me alive.”
 
Prostate cancer is the most commonly diagnosed malignancy, killing about 28,000 men last year. Lung cancer, the second-most common cancer is more deadly and claimed the lives of about 88,000 men. For at least one-quarter of the men whose prostate cancer recurs, the reappearance of the disease is life-threatening, said Eugene Kwon, a urologist and cancer researcher at the Mayo Clinic.
 
Obscured Anatomy
The Mayo Clinic test can be a major step forward in diagnosing prostate cancer recurrence. While widely available MRIs or CT scans can spot bigger growths, the initial small resurgence, when the cancer may be easiest to treat, is often obscured by the structure of the body, particularly if it has been ravaged by surgery or radiation.
 
“It can be difficult to find the forest for the trees,”said Val Lowe, a Mayo radiologist who developed the technique for the medical institution. “This is like turning on a light.”
 
The scanning employs a technique called PET, or positron emission tomography, which uses short-lived radioactive agents that are absorbed by the tissue being studied. Patients are injected with the drug that highlights minute changes in cells consistent with early tumor growth. The Mayo compound is made by attaching a radioactive isotope to choline, a nutrient that cancer cells use as they divide.
 
FDA Approval
The technology was first studied in prostate cancer in 1997 and is still widely used in Europe. While some U.S. hospitals began offering the scan as early as a decade ago, all but the Mayo Clinic, canceled their programs after the U.S. Food and Drug Administration required in 2011 that each hospital go through the drug approval process for its specific imaging agents.
 
The FDA approved Mayo’s application in September 2012 based on its use in 98 men with rising PSA levels and no sign of prostate cancer. More than half the men with abnormalities spotted by PET imaging actually had active cancer. The scan showed doctors where to look, and subsequent biopsies confirmed the tumors.
 
The Mayo imaging agent, called C11 Choline, is the first product the nonprofit medical center has ever taken through the regulatory approval process. It immediately renounced exclusivity, making it easier for others to follow in its path.
 
Logistical Limits
While the approval allows use of the Mayo product anywhere in the U.S., logistics limit its availability. The radioisotopes fused to the choline don’t last long in the body, losing about half their effect within 20 minutes. That means it has to be administered within minutes of its production, restricting availability to the Mayo Clinic campus and making it impractical for pharmaceutical companies to produce and sell the imaging agent.
 
“It’s been hard to commercialize in the U.S. because of the FDA regulations,” said Richard Wahl, director of the division of nuclear medicine at Johns Hopkins Medicine in Baltimore. “Radiopharmaceuticals are viewed almost the same as regular drugs in terms of manufacture.”
 
Other medical centers including Hopkins have worked with Mayo Clinic researchers on collaborative studies. Still, even if medical centers follow Mayo’s exact formula for the product, which costs several thousand dollars, they will have to seek a separate approval from the FDA.

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Promising Compounds
PET drugs were first used in the 1950s as research tools. When promising compounds were discovered, doctors used them in the clinic, giving them to patients to track their disease. The sterile, radioactive drugs generally were made in hospital laboratories that were already equipped with cyclotrons for research. Very few were approved for sale.
 
In 1997, as part of the Food and Drug Administration Modernization Act, Congress gave the FDA directions on how it should regulate the imaging agents used with PET scans. It took the agency 12 years to finalize the rules that would govern the production and ensure they were safe, effective and manufactured properly. The agency further delayed enforcement of the rules until June 2012 to allow doctors and hospitals to prepare.
 
“It is important to ensure these drugs are safe and effective for their intended uses since they will be injected into patients and used to make important treatment decisions,”said Jane Axelrad, chairwoman of the FDA’s PET Working Group.
 
The biggest benefit of C11 Choline may actually be reducing the number of other tests, including blood draws and advanced imaging tests, frequently performed on prostate cancer patients, Kwon said. The PET scan can act as an “easy button,” showing tumors that are local and straightforward to treat, or perhaps so advanced that palliative options are best, he said.
 
“When you think about what the scanner can do, it removes bad random practice, uninformed practice,” he said. “It removes the infinite cycle of ordering expensive tests and never seeing what you are looking for.”

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