For women with metastatic breast cancer who had elevated amounts of circulating tumor cells (CTCs) in their blood after a first line of chemotherapy, switching immediately to a different chemotherapy did not improve overall survival or time to progression. These phase 3 clinical trial results were presented at the 2013 San Antonio Breast Cancer Symposium, December 10-14, 2013.

“We concluded that CTCs are not a good marker in helping to decide when to switch between chemotherapies,” said Jeffrey B. Smerage, MD, PhD, clinical associate professor at the University of Michigan Comprehensive Cancer Center in Ann Arbor. “It had been hoped that switching would both increase the chances of being on an effective therapy and decrease the exposure to toxicity from less effective or ineffective therapies, and as a result, it had been hoped that this early switching would result in improved survival and time to progression (TTP).

“The most important implication is that we have validated that the group of patients with elevated CTCs at both baseline and 21 days [after starting their first chemotherapy] has a worse prognosis with regard to both time to progression and overall survival,” explained Smerage. “Although chemotherapy may work for these patients, it clearly does not work as long as one would like. This suggests that this patient population needs more effective treatment options beyond traditional chemotherapy. Given that these patients have higher cancer-related risks, early consideration of clinical trial participation would be appropriate.”

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About 75% of patients with metastatic breast cancer have CTCs detectable in their blood, and the number of CTCs is elevated in about half of these patients. The presence of elevated CTCs in blood indicates poor prognosis and relatively short TTP, and the goal of this trial was to evaluate if switching to a different chemotherapy is beneficial for patients whose elevated CTCs did not drop after initial chemotherapy.

This trial found that changing therapy for patients with elevated CTCs after one cycle of initial chemotherapy did not improve their overall survival, the primary endpoint of this study.

“An important secondary endpoint was to evaluate whether the levels of CTCs before and after starting a chemotherapy provided prognostic information on how long a patient might live,” Smerage said. “This study confirmed that patients who have low numbers of CTCs before starting chemotherapy have a much better survival. They had a median overall survival of 35 months, which means that half of these patients lived 3 years or longer, and some substantially longer.”

“On the other hand, patients for whom CTCs remained elevated after one cycle of chemotherapy had substantially worse survival. They had a median overall survival of only 13 months,” he explained. “This suggests that chemotherapy may not be as effective for these cancers in which CTCs remain elevated after one cycle of chemotherapy. This doesn’t mean that chemotherapy has no benefit, but it suggests that the benefit is limited.”