New technology has made it relatively easy to detect tumor cells circulating in the blood, which they do when a cancer has spread. A group of researchers tried out the new technique to see if it could tell them anything useful about breast cancer.

What the researchers wanted to know: What is the clinical use of knowing how many cancer cells are circulating in the blood of women with metastatic (spreading) breast cancer?

What they did: At 20 centers in the United States, 177 women with metastatic breast cancer joined the study. Each was about to start a new treatment, but first each had a blood test taken for this study. Three or four weeks after therapy started, another sample was taken. The researchers compared the number of tumor cells in a blood sample to the women's progress over the next nine months or longer. About two thirds of the women were getting chemotherapy, and most of the rest were getting hormonal treatment or immunotherapy. The researchers also used blood from 345 other women as controls; about 150 were healthy (half premenopausal and half postmenopausal), 99 had breast diseases besides cancer, and the rest had other noncancer diseases.

What they found: Five tumor cells in 7.5 milliliters of blood turns out to be a good cutoff. Patients who had that many tumor cells before their treatment started didn't live as long and had their cancers progress faster than patients who had four or fewer tumor cells. Patients with more circulating tumor cells lived a median of 10 months after treatment started, while most patients with fewer lived more than 18 months. Ten patients died before the second blood sample could even be taken, and all had high counts—the worst had 23,618 tumor cells in 7.5 milliliters of blood.

What the study means to you: The number of tumor cells circulating in a breast cancer patient's blood could be a good way to predict whether therapy is likely to work.

Caveats: The study was sponsored by medical device maker Immunicon, which also designed the study in collaboration with the non-Immunicon authors and the FDA, and contributed to the analysis. Immunicon invented the method used to count circulating tumor cells in this study.

Find out more: Immunicon describes its CellSearch technology.

A message board for women with metastatic breast cancer

The National Institute of Environmental Health Sciences is recruiting women whose sisters have had breast cancer.

Read the article: Cristofanilli, M. et al. "Circulating Tumor Cells, Disease Progression, and Survival in Metastatic Breast Cancer." New England Journal of Medicine. Aug. 19, 2004, Vol. 351, No. 8, pp. 781–791.

Abstract online: http://content.nejm.org