CellSearch can be ordered to enumerate circulating tumor cells, but this test is not recommended in the National Comprehensive Cancer Network guidelines, said Peter Ravdin, MD, PhD, a Breast Cancer Researcher and Biostatistician in San Antonio, Texas, and moderator of the press conference where Southwest Oncology Group (SWOG) S0500 results were discussed.

“The study shows that at this time, [circulating tumor cells] cannot be used as a new marker to determine if patients who are failing on one chemotherapy should be switched to another chemotherapy,” Dr. Ravdin said.

“Although this study was negative, intuitively the concept of using elevated [circulating tumor cells] to decide when to switch therapy should work. The study had enormous heterogeneity and was not designed to compare the effectiveness of chemotherapies. Physicians had the choice of front-line therapy and then they switched to another therapy based on circulating tumor cell level. Perhaps if the trial had a cleaner design using specific chemotherapies, the results would have been different,” Dr. Ravdin commented.

“We hope elevated [circulating tumor cells] will be useful in the future. We need uniform and effective second-line therapies. Then we would expect switching early based on [circulating tumor cells], before symptoms develop, would have enormous benefit,” he stated. ■

Disclosure: Dr. Ravdin reported no potential conflicts of interest.