SAN ANTONIO — An elevated circulating tumor cell count at any point during systemic therapy for metastatic breast cancer indicates a high likelihood of rapid disease progression and mortality from that time on, Daniel F. Hayes, M.D., said at a breast cancer symposium sponsored by the Cancer Therapy and Research Center.
This implies that circulating tumor cell count, as measured by a commercially available blood test, may have an important role in patient monitoring and treatment. A randomized prospective clinical trial is now underway to evaluate the impact of switching therapy in patients who develop an elevated circulating tumor cell (CTC) count during therapy, added Dr. Hayes, clinical director of the breast cancer program at the University of Michigan Comprehensive Cancer Center, Ann Arbor.
In a previously reported double-blind multicenter study of 177 women who were about to start a new therapy for metastatic breast cancer, Dr. Hayes and his coinvestigators showed that the presence of at least 5 CTCs per 7.5 mL of whole blood using the CellSearch test was associated with significantly reduced progression-free and overall survival.
The same held true for patients with a positive test at their first follow-up visit after treatment initiation. They had a median 2.1-month progression-free survival from that time, compared with 7.0 months in women with 0–4 CTCs on the test. Their median overall survival was 8.2 months, compared with more than 18 months in those with a negative CellSearch test, said Dr. Hayes, a consultant to Immunicon, the company that developed the test.
In a multivariate regression model, CTC count at baseline and first follow-up visit were the strongest predictors of progression-free and overall survival, outperforming HER2/neu status, tumor receptor status, type of therapy, and other standard predictors (N. Engl. J. Med. 2004;351:781–91).
In Dr. Hayes's new analysis of the same patient cohort, he demonstrated that patients who developed an elevated CTC count at the second, third, or fourth follow-up visit also fared significantly worse than those who continued to have fewer than 5 tumor cells at their blood draw.