Cancer Studies Focus on Early Detection
The survival calculus for many cancers is simple: Find the cancer early on, you live. Find it late, you die.
Yet since Richard Nixon declared ”war on cancer” a generation ago, the lion’s share of attention has gone to figuring out how to treat existing cancers, not working toward earlier detection.
That may be changing.
In recent years the National Cancer Institute has funneled tens of millions of dollars into early detection research. A $144 million program to fund nanotechnology and cancer research will go largely toward searching for new ways to catch cancers early.
”As you begin to look in detail at the genetic makeup of a disease as it evolves, you can see the disease quite a bit before there are any clinical symptoms,” says James Heath, a California Institute of Technology chemist who studies systems for early cancer detection. “Can we develop a diagnostic test that you would do on a really regular basis, even in the home, to catch this?”
A test like this won’t be on the shelf anytime soon, but Heath and others are building prototypes. They rely on ”biomarkers,” specific proteins that show up in the body when cancer is present.
The ideal biomarker would be easily detectable, and both sensitive and specific _ that is, it would always be present when a particular cancer was present, and it would always be absent when that cancer was absent. Alas, the ideal biomarker probably doesn’t exist.
”The challenges facing any biomarker are: Is it sensitive enough to detect cancer early enough to make a clinical impact?” says Dr. Karen Armstrong, whose Harvard lab is searching for breast cancer biomarkers. “Is it specific enough that when it’s abnormal it detects cancer and not something else? And does it really add value to the existing tests that we have?”
Prostate-specific antigen, more commonly known as PSA, is the most important biomarker in use today, and the debate surrounding PSA is indicative of the problems biomarkers can present.
”What PSA lacks is specificity,” says Dr. Mark Soloway, chairman of urology at the University of Miami. In other words, men may have a high PSA but not have cancer.
Another problem with PSA that may plague other biomarkers: Many of the cancers it detects are slow-growing, and not likely to present a problem in older men. That puts many patients in the awkward position of knowing they have a cancer that is best left alone.
Indeed, one recent study found that men who had a PSA test didn’t live any longer than men who skipped it, prompting some experts to question the test’s overall value. That study notwithstanding, Soloway suggests the test has served to heighten men’s awareness of the disease.
”It has clearly changed the pattern if not the face of prostate cancer,” he says. “It’s gotten thousands and thousands of men in the door. … In the days before PSA, in order to detect men with prostate cancer early, you had to do a digital examination. Men are not too excited about that.”
Other biomarkers are in development. A study published earlier this year in the Journal of the American Medical Association found a urine test for a bladder cancer biomarker outperformed the standard techniques of searching for that disease.
And researchers are investigating a biomarker for ovarian cancer, which often progresses undetected.
What will ultimately be necessary, Heath suggests, is a battery of biomarkers that, taken together, present a more comprehensive, clear picture than any single marker _ not only of the presence or absence of a cancer, but also of its stage of development. That will require not only determining which proteins are key, but also developing a mechanism to detect the proteins, which occur in mind-bendingly low concentrations in the blood _ something like one part per hundred billion.
Toward that end, Heath and his colleagues are developing tiny circuits, with transistors a billionth of a meter thick. Each transistor can be attached to an antibody, a biological molecule specially designed to attach to a biomarker. When the antibody binds to the biomarker, the transistor’s ability to conduct electricity changes slightly, signaling the biomarker’s presence.
The long-term goal is to build a circuit _ think of a microscopic computer chip _ that can detect hundreds or thousands of biomarkers in a single test that could catch early cancers that would otherwise go undetected.
”Many existing therapies for some of the worst-case diseases can be quite effective if you can apply them very early,” Heath says. “Many people die of cancer largely because they didn’t even look for it.”
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(c) 2006, The Miami Herald.
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