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MRI advance may detect more cancer

| Thursday, June 19, 2003

BOSTON -- An enhanced type of MRI can detect much smaller tumors than ever before -- some tinier than a pea -- in an advance that could open a new age in diagnosing cancer without surgery, researchers say.

The experimental technique examines the lymph nodes for signs of spreading cancer.

Doctors already routinely use MRIs to check the lymph nodes to see whether cancer that originated somewhere else in the body -- say, in the breast or the prostate gland -- is spreading. But the enhanced technique proved superior to conventional MRIs when tested with cancer that had spread from the prostate.

And the leader of the research, Dr. Mukesh Harisinghani, said his team also has had preliminary success using the approach to detect the spread of breast, testicular, bladder and kidney cancer.

In the prostate study, the technique found 63 cancerous lymph nodes in 33 patients. Conventional magnetic resonance imaging, or MRI, would have missed 71 percent of the nodes, and the spreading cancer would have gone undetected in nine patients.

"Even if it only works this well for prostate cancer, it's a significant advance," said Dr. Jeffrey Brown, a radiologist at Washington University in St. Louis.

Earlier detection of spreading prostate cancer would allow more aggressive treatment sooner, help doctors track the response, and spare some patients unnecessary removal of the prostate gland or lymph nodes. About 200,000 prostate cancer cases are diagnosed each year, and 32,000 people die from it.

The Food and Drug Administration is considering whether to approve the new technique. It is unclear when the FDA might decide.

Dr. Samuel Wickline, who studies imaging at Washington University, said this method and others like it will eventually "allow us to diagnose things that you can't even see with any imaging" now in use.

The study, funded partly by the National Cancer Institute, was carried out by Massachusetts General Hospital in Boston and University Medical Center in Nijmegen, the Netherlands. The findings appear in today's New England Journal of Medicine.

The method relies on minuscule magnetic particles, known as nanoparticles, to enhance an MRI. Acting like a television's contrast dial, the injected particles collect in the immune system's lymph nodes and create a clearer separation between dark and light areas in the image.

Imaging systems have never reliably shown tumors this small before anywhere in the body. Up to now, the smallest tumors detectable by MRI have been about four-tenths of an inch -- the size of a fingernail.

Conventional MRI uses a magnetic field, which allows doctors to see enough only to gauge the size of lymph nodes. Nodes bigger than four-tenths of an inch are generally considered cancerous; however, they are not always cancerous, while some smaller nodes are. The new technique shows detail within the nodes that reveals cancer's presence.

The researchers gave patients an imaging agent known as lymphotropic superparamagnetic nanoparticles, which are specks of iron oxide less than a billionth of an inch across. Normally, the liver sucks up imaging agents before they reach the lymph nodes, but these particles are so small, they seep into the lymph system.

The technique appeared to work in cancerous lymph nodes from two-tenths to four-tenths of an inch, which would normally go unnoticed with regular MRI. It detected 96 percent of cancerous nodes that size, compared with a detection rate of 29 percent for regular MRI, and it found 41 percent of cancerous nodes smaller than two-tenths of an inch, which are invisible to conventional MRI.

When spreading cancer has already reached the lymph nodes, doctors typically order radiation or hormonal treatments.

The researchers did not report any major side effects from the imaging agent.

"I would anticipate that it's going to get approved, and I would anticipate that it's going to be a big seller," said Dr. Otis Brawley, a cancer specialist at Emory University in Atlanta.

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