Early chemo switch not beneficial in patients with high circulating tumor cells

In patients with metastatic breast cancer who failed to clear circulating tumor cells (CTCs) after one cycle of first-line chemotherapy, switching to a different chemotherapy does not improve survival or delay progression, the phase III SWOG S0500 trial has shown.    

“It had been hoped that early switching of chemotherapy would result in improved survival and time to progression. However, based on our results, we conclude that CTCs are not a good marker in helping to decide when to switch between chemotherapies,” said study author Dr. Jeffrey Smerage of the University of Michigan Comprehensive Cancer Center, Ann Arbor, Michigan, US. [Abstract S5-07]

In the study of 595 patients, 319 had elevated CTCs (≥5 CTCs/7.5 mL whole blood) at baseline. After one cycle of first-line chemotherapy (ie, 21-day follow-up), 123 patients continued to have elevated CTCs. These patients were randomized to continue with initial chemotherapy or switch to a second-line chemotherapy in the second cycle.

“The outcomes were similar between patients who continued first-line therapy and patients who switched therapy,” reported Smerage. “Median overall survival (OS) was 12 months in both arms (hazard ratio, 1.01). Progression-free survival (PFS) was 3.5 months in patients who continued therapy and 4.6 months in those who switched therapy (hazard ratio, 0.91).”

The study also confirmed the prognostic value of CTC levels in patients with metastatic breast cancer. “Patients with low CTC levels before starting chemotherapy had a much longer median OS of 35 months. In contrast, patients with elevated CTC levels at baseline and 21 days had substantially worse survival,” Smerage noted.

About 75 percent of patients with metastatic breast cancer have detectable CTCs in blood. In about half of these patients, the number of CTCs is elevated.

“Several groups are investigating the presence of biomarkers such as estrogen receptor and human epidermal growth factor receptor 2 on CTCs,” smerage added. “Measurement of these biomarkers will hopefully allow better prediction of what therapies work best for these patients.”