Patients with breast cancer receiving aspirin have decreased plasma IL-8 levels and platelets with impaired metastatic potential. (A) Tumor tissue from aspirin-treated or non-aspirin–treated (control) mice bearing MCF-7ras tumors was collected and stained for human IL-8 by immunohistochemistry. Tumors from 5 separate 100 mg/kg aspirin-treated mice and 5 control mice are shown, and semiquantitative analysis performed based on optical density. Platelets and plasma were isolated from patients with breast cancer (BC) who were either taking or not taking aspirin (81-325 mg/d). Plasma levels of soluble p-selectin (B), CCL5 (C), and IL-8 (D) were then measured by ELISA. Platelets isolated from patients were exposed to MDA-MB-231 breast tumor cells; APR was collected and used for the following: APR CCL5 measured by ELISA (E), APR was used to treat MDA-MB-231 cells for 24 hours and IL-8 secretion was measured by ELISA (F), and APR was used in Matrigel invasion assays with MDA-MB-231 cells (G-H). Scale bars represent 100 μm. P values were obtained through separate 1-way ANOVA, with post hoc Tukey’s multiple comparisons testing. n = 7 to 9 independent replicates per treatment group in panels B-D and 3 to 6 independent replicates per treatment group in panels E-F and H.