Fishing for Tumors

Tumors can betray their presence by shedding cells that enter the bloodstream. Spotting these rare cells takes a keen eye and good luck, but now researchers have devised a tool that ups the odds of detection. The technique, described in tomorrow's Proceedings of the National Academy of Sciences, may eventually help physicians diagnose tumors sooner than current techniques can--well before metastasis can take hold and thwart effective therapies.

Cells sloughed by tumors comprise only a minute fraction of blood or bone marrow, so scientists must meticulously comb through thousands of cells to find a few cancerous ones. Jonathan Uhr, a microbiologist at the University of Texas Southwestern Medical Center at Dallas, and his colleagues wanted to create an accurate census by fishing out cancer cells.

For bait, the researchers coated submicroscopic iron particles with antibodies that bind to specific types of cancer cells. Next they mixed the bait with blood samples from 33 patients with breast or prostate cancer and from 13 healthy people. Exposing the samples to a magnetic field for a total of 15 minutes made the iron-bound cells migrate together, allowing the scientists to extract a portion of the sample in which the cancer cell concentration had been boosted approximately 10,000-fold.

Using a technique called flow cytometry, in which a laser beam shot through a single-file stream of cells reveals clues to their size and make-up, the researchers were able to identify and precisely tally each sample's cancer cells in as little as 2.5 hours. The technique found that suspicious cells, as expected, were much more numerous in all the cancer patients than in the healthy individuals. Further testing ruled out cancer in the healthy controls. This cancer cell count would not have been possible using traditional techniques, the researchers say.

"It's precisely the kind of assay that we have been needing" to nab circulating cancer cells more effectively, says David Bruns, a pathologist at the University of Virginia in Charlottesville. Uhr's group will next monitor people at high risk, such as women with a family history of breast cancer, and test the method's ability to spot tumor cells at the earliest stages of cancer development.