Chemotherapy given every two weeks rather than the usual every three weeks significantly delays relapses and improves survival in breast cancer patients, according to researchers at Memorial Sloan-Kettering Cancer Center in New York.

Researchers believe these findings may lead to major changes in treatment of breast cancer.

Physicians have used the three weeks between treatments course of chemotherapy in part because the drugs cause a sharp decrease in white blood cells that fight infection and also to give the body a longer period to recover between treatments.

Researchers conducted a study of 2,005 women treated for breast cancer in hospitals across the country between 1997 and 1999. The average age of the patients was 50 years old.

Women who were given the more frequent doses of chemotherapy were also given Neupogen, a drug that stimulates the body to produce white blood cells, allowing the white blood cell count to recover faster.

In women getting the more frequent treatment, only 18 percent had a cancer recurrence within four years, compared with 25 percent of women receiving the standard treatment. Only eight percent of the more frequently treated women died within three years, compared to 10 percent of the women receiving the usual treatment.

Women getting the more frequent treatment had fewer episodes of low white blood cell count than women getting the standard treatment who were not given Neupogen. The more frequent doses of chemotherapy did not increase toxicity but did increase the need for blood transfusions, according to the study presented at the San Antonio Breast Cancer Symposium.

Researchers speculate that the more frequent chemotherapy may work better because it gives the tumor cells less time to grow back before being treated with the drugs again.

Other sources: San Antonio Breast Cancer Symposium, New York Times