Lack of platelet GPVI inhibits tumor metastasis. (A) Schematic of a lung colonization assay after IV injection of MC38 colon (B,D) or AT-3 breast (C,E) cancer cells in WT and Gp6^−/− mice. (B,C) Representative photographs (top) and hematoxylin-eosin–stained sections (bottom) obtained from the lungs of MC38 and AT-3–injected WT and Gp6^−/− mice. (B,C) Dashed black circles and arrows indicate metastatic nodules. The bar represents 200 µm. (D,E) Bar graphs representing the number of lung metastases in MC38 (D)- and AT-3 (E)–injected WT and Gp6^−/− mice. Mean ± standard deviation (SD); n = 5 (D) and n = 7 (E) mice per group. ***P < .001, by unpaired Student t test. (F,I) Schematic of mouse heterotopic and orthotopic metastasis assays. MC38 (F-H) and AT-3 (I-K) tumor cells were injected subcutaneously or into the fourth mammary fat pad of WT and Gp6^−/− mice, and the volume of subcutaneous (G) or mammary (J) tumors and the number of lung metastases was determined. (G,J) Kinetic of primary tumor growth in WT and Gp6^−/− mice. Mean ± SD; n = 5 (G) and n = 8 (J) per group. (H,K) The number of spontaneous lung metastases in MC38 (H)- and AT-3 (K)–injected WT and Gp6^−/− mice. Mean ± SD; n = 6 (H) and n = 8 (K) mice per group. *P < .05; **P < .01, by Mann-Whitney test.