Platelet trafficking in experimental breast cancer. (A) Systemic platelet count as well as a proportion of aged platelets of total platelets in the peripheral blood of tumor-free control or orthotopic 4T1 tumor-bearing mice as assessed by flow cytometry; quantitative data are shown (mean ± standard error of the mean [SEM] for n = 3-4 mice per group; ∗P < .05 vs control). (B) Representative confocal microscopy images of GPIbβ⁺ platelets (white) in the intra- and peritumoral microvasculature of 4T1 tumors (tdTomato-transduced fluorescent tumor cells; red) and lungs, brain, kidneys, and liver (parenchymal structure in blue; scale bars: 100 μm) harvested from 4T1 tumor-bearing mice. (C) Interactions of platelets (white), endothelial cells (EC; broken lines), and leukocytes (green) in the peri- and intratumoral microvasculature of 4T1 tumors (blue) implanted into the auricle as assessed by in vivo microscopy, a representative image (scale bar: 10 μm) and quantitative data for the tumor microvasculature and the tumor-free auricular microvasculature are shown (mean ± SEM for n = 6 mice per group; ∗P < .05 vs control). (D) Proportion of neutrophils, monocytes, and lymphocytes bound to platelets of total neutrophils/monocytes/lymphocytes in the peripheral blood of mice 10 days after 4T1 tumor induction; quantitative data are shown (mean ± SEM for n = 10 mice per group; ∗P < .05 vs control). (E) Proportion of leukocytes bound to procoagulant platelets (phosphatidylserine⁺ GPIbβ⁺ cells) of leukocytes (CD45⁺ cells) bound to platelets (GPIbβ⁺ cells) accumulating in the intra- and peritumoral microvasculature, quantitative data and a representative in vivo microscopy image is shown (mean ± SEM for n = 3 mice per group).