A study conducted in China has confirmed the utility of measuring circulating tumor cells (CTCs) to predict outcomes and response to therapy in women with metastatic breast cancer, including those with newly diagnosed disease and HER2-positive or triple-negative disease.1
CTCs are cancer cells that have detached from the tumor and circulate in the bloodstream. Previous studies have established that CTCs are strong predictors of progression-free survival (PFS) and overall survival (OS) in metastatic breast cancer, but retrospective analysis questioned their prognostic value in newly diagnosed women with HER2-positive or triple-negative tumors.
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The prospective, double-blind study recruited 300 patients with metastatic breast cancer who were starting a new course of systemic therapy; additionally 99 patients recruited were healthy women with no history of cancer, and 101 women were diagnosed with benign breast disease. CTCs were measured using the Cellsearch® system (Janssen Diagnostics).
CTCs were rare in the control patients, none of whom had more than two CTCs in 10 mL of blood. By contrast, 115 patients with metastatic breast cancer had five or more CTCs.
Measuring CTCs yielded good prognostic data: compared with patients who had fewer than five CTCs at baseline, those with five or more CTCs at baseline had significantly shorter PFS (6.7 vs. 9.0 months, respectively) and OS (13.2 vs. 24.6 months, respectively).
CTC measurement also was useful in evaluating response to therapy. Patients with fewer than five CTCs after a course of therapy had significantly longer median PFS (8.2 vs. 5.9 months) and OS (20.1 vs. 12.4 months) than patients with five or more CTCs.
At a follow-up imaging visit, 79 patients were found to have had a complete or partial response to therapy. Of these, 33 patients had more than five CTCs before therapy and seven patients had more than five CTCs after therapy. Of the 30 patients found to have progressive disease, 15 had five or more CTCs before therapy; no change in CTC count was found in any of the 15 patients after therapy.
The Cellsearch system also proved to be valuable among newly diagnosed patients with metastatic cancer. Of the 119 newly diagnosed patients, 45 had five or more CTCs at baseline. These patients had significantly shorter mean PFS (8.7 vs. 12.3 months) and OS (14.6 vs. >24.6 months) compared with the 74 newly diagnosed patients with fewer than five CTCs at baseline.
CTC measurement was also effective at predicting outcomes in patients with HER-2-positive cancers. Of the 104 patients in this subset, the 29 who had five or more CTCs at baseline had shorter PFS (6.7 vs. 7.9 months) and OS (11.3 vs. >24.5 months) compared with those who had fewer than five CTCs at baseline.
Patients with triple-negative breast cancer and five or more CTCs at baseline had shorter PFS and OS than those with fewer than five CTCs; the differences among the groups did not reach statistical significance due to small sample sizes.
“In China, the incidence of breast cancer has increased rapidly in recent years, in part due to changes in reproductive patterns, obesity, physical inactivity and local breast cancer screening efforts,” said lead study author Zefei Jiang, MD. “These results in HER2-positive patients are very important since the anti-HER2 diagnostics and treatment situation in China is different from many parts of the world due to economic constraints and available technology.”
Reference
1. Jiang ZF, Cristofanilli M, Shao ZM, et al. Circulating tumor cells predict progression-free and overall survival in Chinese patients with metastatic breast cancer, HER2-positive or triple-negative (CBCSG004): a multicenter, double-blind, prospective trial. Ann Oncol. 2013; July 14 [Epub ahead of print] doi:10.1093/annonc/mdt246.
