Counting the number of tumor cells that have broken away from a tumor and are circulating in the blood can help doctors choose between chemotherapy and endocrine therapy for patients with metastatic breast cancer, according to a study presented at the recent San Antonio Breast Cancer Symposium

Currently, doctors tend to use all available endocrine therapies, such as the drug tamoxifen, before switching to chemotherapy to treat metastatic breast cancer, said study author François-Clément Bidard, MD, PhD, a professor of medical oncology at Institut Curie and Versailles Saint-Quentin University in Paris, at a press conference.

Circulating tumor cell count, or CTC as it’s also known, has been extensively studied for the treatment of metastatic breast cancer in the past two decades to see whether it can help fine-tune treatment, Dr. Bidard said.

In study presented at the conference, the researchers reported that patients with metastatic, estrogen receptor (ER)–positive/HER2-negative breast cancer who were treated based on their CTC count had better long-term outcomes. In a group of women in the study whose doctors recommended endocrine therapy but who had a high CTC count, those treated with chemotherapy instead had a median longer survival of 16 months and a 47 percent reduction in their risk of death compared with patients in the same group who received endocrine therapy.

This study is a follow up to one published by Bidard and his colleagues in 2018 (PDF). In it, 755 patients were randomly assigned to having their treatment decided by the investigator or by their CTC count. The early results, reported in 2018, showed longer survival without progression of the cancer in those patients who were given chemotherapy instead of endocrine therapy based on their CTC counts.

Among the subgroup of patients who were treated with chemotherapy as decided by their doctors but had a low CTC count, (14 percent of the study participants) those who received endocrine therapy had a comparable overall survival to those who received chemotherapy.

"Our study demonstrates that integrating prognostic biomarkers into the treatment algorithm can improve the management and outcomes of metastatic breast cancer patients," said Bidard.

At the press conference, expert commentators noted that a CTC count, which requires a specialized exam, isn’t always routinely done. Women may have to ask for the test, said SABCS co-director Carlos Arteaga, MD, director of the UT Southwestern Harold C. Simmons Comprehensive Cancer Center in Dallas, who was at the press conference.