A new test allows caregivers and breast cancer patients to learn in weeks, instead of months, whether treatment is working, a recent study indicates. Called the CellSearch System, the test counts metastatic cancer cells contained in a blood sample from a patient with breast cancer.

Researchers performed the test on 177 women with stage IV breast cancer before they started therapy and at their first follow-up visit after therapy started. Forty-nine percent of the women had five or more circulating tumor cells per 7.5 ml of blood.

Compared with women who had fewer than five circulating tumor cells per 7.5 ml of blood, these patients had significantly shorter rates of progression-free survival (about 3 months versus 7 months) and overall survival (10 months versus over 18 months). Test results were similar at the first follow-up visit.

Researchers concluded that the number of circulating tumor cells detected before treatment can predict rates of progression-free and overall survival. Future research will study women with less-advanced breast cancer and patients with other cancer types.

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