Can stopping blood clot formation reduce circulating tumor cells?

This study investigated the effect of a combined therapy of aspirin and clopidogrel on circulating tumor cells in patients with metastatic breast cancer.

Circulating tumor cells or CTC (cancer cells that have migrated from the tumor and are circulating in the blood stream) are known to play an important role in the development of distant metastases (cancer spread in distant organs and tissues of the body) in patients with cancer. In contrast to clinically overt metastases, circulation of tumor cells in the bloodstream can be detected much earlier. Platelets are part of the blood cells and, when aggregated, they form blood clots. It is known that increased blood clotting is associated with malignancy. Previous studies have shown that antiplatelet therapy (drugs that stop the aggregation of platelets) such as aspirin or clopidogrel added to chemotherapy in patients with lung cancer can prolong survival and the remission period. This study examined whether a combined treatment of aspirin and clopidogrel may reduce the number of CTCs in patients with metastatic breast cancer, by decreasing the clotting ability of platelets. 

48 women with metastatic breast cancer that were not under current chemotherapy were included in this study. 24 women were randomly assigned to receive aspirin and clopidogrel therapy (intervention group), while the other 24 patients did not receive any treatment (control group). During the study, some patients have withdrawn from the research due to bleeding, which is known to be a side effect of the drugs. Only 19 patients from the intervention group and 23 from the control group were evaluated at 1 month. CTC blood levels and platelet aggregation function were evaluated through blood sample tests at the beginning of the study (baseline), at 2 weeks and at 1 month.

Results showed that at baseline, 65% of all patients had 1 or more CTCs and 13% had 5 or more CTCs. At the end of one month of treatment, despite adequate platelet inhibition, there was no significant difference in CTC number between the intervention and the control group. There were no severe bleeding side effects reported during the study period.

In summary, platelet activity inhibition with aspirin and clopidogrel failed to decrease the blood levels of CTC in patients with metastatic breast cancer. 

The starting point of the study included patients with already low CTC values at baseline. This may explain the why the treatment was not beneficial. Further studies should be conducted including patients with higher CTC levels. Moreover, the study group and follow up period were very small. 

Circulating tumor cells is an important predictor of metastasis. Consult your physician about CTC evaluation.