The Cancer Test

By Alice Park

With a disease as complex as cancer, it's easy to forget that sometimes the most effective defense can be the simplest. Despite all the gadgets that modern medicine has to image, diagnose and track a tumor, there is an easier way to go about things. Researchers at the American Society of Clinical Oncology (ASCO) conference in Chicago reported earlier this month that the best way to figure out how a cancer is progressing is to draw a little blood.

Tracking cancer via the blood certainly isn't new. Just as a pregnancy test can detect the proteins of a 10-day-old fetus in the mother's circulatory system, similar tests can detect proteins on cancer cells released by a tumor that is itself only dozens of cells large. Most of these migrating cells die during the journey. Others are more menacing--pioneers programmed to seed new growth in distant tissues. Either way, as epithelial cells--closely packed, multilayered cells of which most solid tumors are made--they are oddballs in their new fluid environment. "It's like splitting a deck of cards into red and black suits," says Dr. Daniel Hayes, director of the breast-cancer program at the University of Michigan, about separating these epithelial tumor cells from the blood. "Blood is made up of different tissues, so we look for epithelial cells that shouldn't be there."

But those tests take you only so far. Suppose you could do more than just collect the enemy cells. Suppose you could interrogate them for information. That's what the new tests make possible. Researchers are starting to identify, for example, proteins on the surface of tumor cells that might signal a faster-growing, more aggressive type of cancer. Other protein signatures may hint at a more advanced tumor that is poised to metastasize. Both can help doctors craft more personalized therapies that match the right treatments to the right patients at the right time, improving effectiveness, lowering the costs of hit-or-miss treatments and reducing toxic side effects.

"We can look at tumors for changes at the DNA, RNA and protein levels," says Dr. Gordon Mills, chair of systems biology at the M.D. Anderson Cancer Center in Houston. "It certainly gives us a way of looking at what is happening inside a tumor, and that's very exciting."

Perhaps the biggest appeal of these assays, however, has to do with their ease and simplicity. Currently, doctors seeking the same information must collect a sample of the tumor tissue, something that isn't always possible if it's very small or inaccessible or its precise location isn't known. Then there is the danger that the physical act of tissue sampling can dislodge cells and cause them to spread the disease. A blood draw bypasses all these risks.

Even without such sophisticated genetic work, doctors can now learn more about how treatment is progressing simply by tallying the number of circulating cancer cells and better understanding what that head count means. At the ASCO conference, researchers from the U.S., Britain and the Netherlands reported that after about a month of treatment, patients who had advanced prostate and colon cancers and lower circulating cell counts survived an average of twice as long as those who had higher levels. More cells in the blood could be a sign that the drugs are not working and that it's time for a different chemotherapy regimen. Such blood-based diagnostics may not yet have beaten cancer, but, says an enthusiastic Mills, they "are the holy grail." Those are decidedly optimistic words in a specialty too often short on them.