Scientists have developed methods to more accurately predict the course that two common types of cancer are likely to take. They have devised ways to forecast whether breast cancer will spread. They have also found ways to determine who has colon cancer or who is at risk of getting it. The findings employ new technology that detects molecular markers in cancer.

First, the breast cancer study.

U.S. and Dutch scientists say their new genetic screening technique could take much of the mystery out of predicting whether a breast cancer tumor will spread to other parts of the body.

The disease spreads differently in different patients. The researchers report in the journal "Nature" they have found a specific pattern of genes in aggressive tumors that spread quickly.

Netherlands Cancer Institute researcher Laura van't Veer and U.S. colleagues found the pattern by analyzing genes in 78 breast cancer tumors from women and correlating them with their later outcomes. "By looking at the gene activity pattern of 25,000 genes, we found that 70 genes could foretell whether a woman had a high chance to develop a distant metastasis, or whether there was a high chance that the disease would not come back," she says.

The scientists have created a breast cancer tumor gene classification system they say can predict whether secondary tumors will appear with an 80 percent accuracy.

Current diagnostic tools are much worse predictors. Therefore, many patients receive toxic follow-up treatments for potential tumor spread when they don't need them. Cambridge University cancer specialist Carlos Caldas says the gene profiling method, if confirmed in larger studies, would better target only those who need the additional therapy. "This represents effectively the first step towards individualized cancer treatment," he says. "By that, I mean that you'll give patients treatment based on the genes that are expressed in their cancer."

Dr. Caldas notes that genetic profiling is not limited to breast cancer. Massachusetts researchers recently reported a similar system to predict the outcome of the most common type of childhood brain tumor. Michigan doctors have found genetic markers for prostate cancer prognosis. "I have no reason to believe that this will not be able to be applied to all cancers," he says.

In another study, in the New England Journal of Medicine, researchers at the Johns Hopkins University in Baltimore report a reliable, noninvasive genetic test to detect colon cancer at its earliest, curable stages. It analyzes stool samples for the presence of known genetic mutations in the cancer.

Johns Hopkins scientist Giovanni Traverso says the test is a more comfortable alternative to current methods, such as the colonoscopy. "The general population generally does not request the appropriate screening," he says. "The reason why people aren't getting tested is that the current tests available are quite invasive. All of these tests that do exist are very effective. What we have done is basically provide another option."

Analyzing 74 stool samples, the researchers detected the telltale genetic mutation in 61 percent of those with early colon cancer, half of those with precancerous lesions, and none in those who were disease free.

Mr. Traverso says the new test should detect a high percentage of people developing colon cancer, although people at higher than normal risk should still have the more reliable colonoscopy.

Both the colon cancer and breast cancer tests are the result of the cancer research revolution. The head of the American Society of Clinical Oncology, Dr. Charles Balch, says new methods can identify and target the underlying molecules that promote the disease. "We often make the diagnosis and plan our treatment using molecular markers, including the ability to specifically diagnose which cancer genes are present and their products that now reveal unique aspects of vulnerability that can drive our treatment," he says.

Dr. Balch says such precision makes cancer diagnosis and treatment more specific and reliable than older methods.