Blood Test May Help Detect Cancers Earlier

Method Uses Magnets to Concentrate Cells Shed by Tumors for Better Analysis

A sensitive new blood test could help doctors find tumors sooner and improve monitoring of treatment, researchers say.

"The idea is to detect cancers earlier, when they're more treatable," said Jonathan Uhr of the University of Texas Southwestern Medical Center at Dallas. Emilian Racila, one of his colleagues, noted that some breast cancers can grow for years before becoming large enough to be detected by mammography.

The new test, which uses magnets to concentrate cancer cells from blood, is reported in today's issue of Proceedings of the National Academy of Sciences. The test has been used on patients with breast and prostate cancer. Tests on other tumors are planned.

Carleton Stewart of Roswell Park Cancer Institute in Buffalo, N.Y., who did not participate in the research, termed their results "extremely positive." He said similar research is underway at his hospital.

"It is not only a means of early detection and monitoring, but it can have a significant impact on treatment plans for the patient. If one knows that the patient has circulating [cancer] cells, they may require a different kind of treatment than one who doesn't," he explained.

Uhr cautioned that "a year or two of further study" is needed to determine if the test will help physicians deal with individual patients.

Doctors have long known that tumors shed cells into the bloodstream, but it takes many such cells to be detected. The new test lets doctors detect a single cancer cell in a small blood sample. Tiny iron particles coated with an enzyme that attaches itself to certain kinds of cancer cells are placed in the blood sample. Magnets are then used to concentrate the cancer cells, which can then be studied.

The test locates epithelial cells, a type of cell that forms the skin, glands and other tissues but is rarely present in the bloodstream. Breast and prostate cancers tend to grow slowly, but shed these cells from their early development, Racila explained. While a breast tumor might need 100 million cells before it could be found in a mammogram, a tumor of 1 million cells could shed enough epithelial cells into the blood to be detected, Racila said.

The researchers found that blood samples from 13 healthy people averaged just 1.5 epithelial cells per sample. By comparison, 14 patients with breast cancer that had not spread averaged 15.9 epithelial cells. Five with cancer that had spread locally averaged 47.4 cells and 11 patients whose cancer had spread to other parts of the body averaged 122 cells.

They also tested three prostate cancer patients, who averaged 16 epithelial cancer cells per blood sample.

Besides offering the hope of earlier detection for these cancers, Uhr said the researchers want to see if the test works for cancers of the colon and intestinal tract, which are harder to detect with traditional methods.

They also hope the test will be useful in following the progress or cancer treatment by determining if the number of epithelial cells in the blood declines. Any sudden increase after treatment ends could warn of impending relapse.

"One advantage of this method is that we can count the number of cancer cells in the blood, and it appears to be correlated in general with the extent of the tumor," Uhr said. "By counting the cells and characterizing them it may be possible to predict the progressive states of the disease."