Blood Test May Open New Doors on Cancer
In a major report released today, researchers at Harvard Medical School said they have found a blood test that may open up an entirely new approach in diagnosing a wide variety of cancers.
The test uses a promising technique, called nuclear magnetic resonance spectroscopy, which may lead to very early detection of tumors and the prediction of which tumors will spread.
The experimental test measures the mobility of fat molecules in the bloodstream, which appears to be increased by the presence of tumors. It differs from previous blood tests which measure tumor proteins that enter the bloodstream.
In preliminary experiments, spectroscopy picked up abnormalities in 81 patients known to have malignant tumors. It “reliably distinguished” them from 44 normal individuals, 60 patients with other diseases and from all but one of 38 patients with benign tumors who served as controls, according to a report in the New England Journal of Medicine.
The report said such measurements “may be applicable to many--perhaps all--types of cancer.”
“This is something new in diagnosing cancer,” said Eric T. Fossel of the Beth Israel Hospital in Boston, the principal author of the study.
While the report is sure to generate enthusiasm, spectroscopy needs “considerably more testing” before it can be widely used, Fossel said.
Like the handful of previously identified blood markers for tumors, the technique lacks specificity--it was not able to distinguish the blood of cancer patients from that of pregnant women or men with enlarged prostate glands.
Clinical Trials Urged
The technique was also not able to determine the type or location of a tumor or to monitor the response of patients with malignant tumors to therapy.
The report calls for clinical trials, “including greater numbers of patients in whom cancer is not suspected,” to determine the value of the technique for early diagnosis. Generally, the earlier treatment can begin, the greater chances of success. Current techniques usually fail to detect tumors unless they are at least one centimeter in diameter; but by then, a tumor already contains one billion cancer cells.
“We think spectroscopy will be clinically useful in the future,” said Dr. William G. Bradley of the Huntington Medical Research Institutes in Pasadena, another researcher in the field. “At this point, to say that spectroscopy is a clinical tool is going a little too far.”
The Harvard study is the latest in a series of recent experiments relating cancers to changes in fat molecules, called lipoprotein lipids, in the membranes of cancer cells and in the bloodstream as well.
One theory is that cancer cells make unique fat molecules, which are in turn shed into the blood stream. Another is that the changes are a response by the patient’s body to the presence of a tumor.
In 1985, Andreas J. Wieczorek of the University of Munich isolated a complex of fats and proteins from the blood of patients with a wide variety of tumors, which did not appear in patients with nonmalignant tumors or in healthy people.
This year, Lesley C. Wright of the University of Sydney in Australia used NMR spectroscopy to show that this fat complex could be detected in cancer cells and specimens of tumors removed at surgery.
In related studies, Dr. Ian C. P. Smith of the National Research Council in Ottawa, Canada, is using NMR to predict the potential of human ovarian or colon cancers to spread throughout the body.
Could Be ‘Phenomenal’
“These techniques could be phenomenal for the routine screening of patients or the management of cancer patients after diagnosis,” Smith said in a telephone interview. Other potential applications include choosing cancer drugs and distinguishing between benign and malignant tumors, he said.
In the experiments in Boston, blood samples were obtained from patients and centrifuged to separate the blood cells from the plasma fluid. The plasma was then analyzed.
NMR spectroscopy was used to measure the time it took hydrogen atoms in the patient’s lipoproteins to slow down after they were excited by radio wave pulses. The measurement techniques have been developed through basic research by chemists and physicists over several decades.
Fossel believes that the hydrogen atoms take longer to slow down in cancer patients than in normal individuals because of a mysterious increase in the mobility of their fat molecules.
Takes Five Minutes
“It is not a unique substance to cancer,” Fossel said in a telephone interview. “It is a difference in how the lipid molecules are put together and assembled.”
NMR testing of the plasma takes about five minutes, according to Fossel. He predicted that if the testing proves valuable, it could be automated and made available for “about $50 a test.”
But Smith said it is “a little naive” to think that NMR testing would be widely available. The sophisticated computerized instruments, which contain powerful magnets, may cost $1 million or more. Instead, he predicted that spectroscopy would be most useful as a research tool, facilitating the development of new conventional diagnostic tests for cancer and other diseases.
NMR spectroscopy is closely related to magnetic resonance imaging, a non-invasive scanning technique that has already rendered obsolete some uses of the X-ray and simplified the diagnosis of multiple sclerosis and other nervous system disorders.
In addition to cancer, researchers are using NMR spectroscopy to study abnormalities in the muscles of the arms and legs and to distinguish normal heart tissue from tissue with an inadequate blood supply, according to Dr. Earl P. Steinberg of the Johns Hopkins Medical Center.
