Platelets lacking PITPβ or both PITP isoforms are less susceptible to tumor metastasis. (A,B) Lungs harvested from Pitpβ^fl/flPf4-Cre^- and Pitpβ^fl/flPf4-Cre⁺ mice (A) or Pitpα^fl/fl/β^fl/flPf4-Cre^- and Pitpα^fl/fl/β^fl/flPf4-Cre⁺ mice (B) 2 weeks after tail vein injection with B16F10 melanoma cells demonstrated that loss of PITP impairs metastasis. Representative lungs are shown at 2 weeks after tumor cell injection (top); the number of tumor nodules on the lung surface 2 weeks after tumor cell injection (middle); and wet lung weights 3 weeks after tumor injection (bottom). For tumor nodule counting, n = 21 lungs for Pitpβ^fl/flPf4-Cre^- mice, n = 19 for Pitpβ^fl/flPf4-Cre⁺ mice, and n = 13 for both Pitpα^fl/fl/β^fl/flPf4-Cre^- mice and Pitpα^fl/fl/β^fl/flPf4-Cre⁺ mice. For lung weight, n = 21 lungs for Pitpβ^fl/flPf4-Cre^- mice, n = 20 for Pitpβ^fl/flPf4-Cre⁺ mice, n = 17 for Pitpα^fl/fl/β^fl/flPf4-Cre^- mice, and n = 18 for Pitpα^fl/fl/β^fl/flPf4-Cre⁺ mice. Statistical analysis was performed using an unpaired t test. Black scale bars represent 10 mm. (C,D) Ex vivo adhesion of PITPβ-null (C) or PITPα/β-null (D) platelets to a tissue-cultured tumor cell monolayer was impaired compared with wild-type controls. Error bars represent s.d.; n = 3 for each genotype.