title: A randomized phase II trial investigating the effect of platelet function inhibition on circulating tumor cells in patients with metastatic breast cancer.
abstract: BACKGROUND
  Blockade of platelet activation and aggregation can inhibit metastasis in preclinical models and is associated with cancer prevention. To test whether disruption of platelet function with clopidogrel and aspirin would decrease the number of circulating tumor cells (CTCs) in patients with metastatic breast cancer, a randomized phase II study was performed.
  
  
  METHODS
  Patients with metastatic breast cancer who were not currently receiving cytotoxic chemotherapy were eligible. Patients were randomized to receive either clopidogrel and aspirin or to a control group receiving no treatment. Phlebotomy was performed at baseline, at 2 and 4 weeks, and monthly thereafter to obtain specimens to assess CTC, platelet aggregation, and thrombin activity. The primary end point was the proportion of patients with detectable CTCs at 1 month.
  
  
  RESULTS
  Forty-eight patients were enrolled and 42 were evaluable at 1 month. Baseline CTC numbers were ≥ 5 in 13% and ≥ 1 in 65% of patients. Despite adequate platelet function inhibition in the treatment group, the proportion of patients with detectable CTCs was similar between the clopidogrel/aspirin and control groups at baseline (P = .21) and 4 weeks (P = .75), showing no treatment effect. Measured endogenous thrombin potential did not correlate with CTC number. No bleeding-related serious adverse events (SAEs) occurred.
  
  
  CONCLUSIONS
  The baseline CTC numbers were lower than expected, decreasing the ability to detect an impact of platelet inhibition on CTCs. Clopidogrel and aspirin were well tolerated. Future studies evaluating the potential therapeutic role of antiplatelet therapy in breast cancer remain of interest, and they may be informed by these results.
authors.affiliation: Department of Medicine, Division of Oncology, Washington University School of Medicine in St. Louis, St. Louis, MO.
authors.forename: Ryan P
authors.initials: RP
authors.lastname: Roop
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Naughton
authors.forename: Catherine
authors.initials: C
authors.lastname: Van Poznak
authors.forename: Jochen G
authors.initials: JG
authors.lastname: Schneider
authors.forename: Philip E
authors.initials: PE
authors.lastname: Lammers
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Pluard
authors.forename: Farley
authors.initials: F
authors.lastname: Johnson
authors.forename: Charles S
authors.initials: CS
authors.lastname: Eby
authors.forename: Katherine N
authors.initials: KN
authors.lastname: Weilbaecher
mesh_terms: D001241:Aspirin / Q000627:therapeutic use*; D001792:Blood Platelets / Q000187:drug effects*; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000473:pathology; D016022:Case-Control Studies; D000077144:Clopidogrel; D004359:Drug Therapy, Combination; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008875:Middle Aged; D009362:Neoplasm Metastasis; D009360:Neoplastic Cells, Circulating / Q000187:drug effects*; D015539:Platelet Activation / Q000187:drug effects*; D010974:Platelet Aggregation / Q000187:drug effects*; D010975:Platelet Aggregation Inhibitors / Q000627:therapeutic use*; D011379:Prognosis; D013988:Ticlopidine / Q000031:analogs & derivatives* / Q000627:therapeutic use; D016896:Treatment Outcome
chemical_list: D010975:Platelet Aggregation Inhibitors; D000077144:Clopidogrel; D013988:Ticlopidine; D001241:Aspirin
keywords: Breast cancer; Circulating tumor cells; Platelet inhibitors