We found that the pkcα‐/‐ platelets, which have normal platelet counts (Figure S8A) and GPIbα expression (Figure S8B) in the platelets, showed lower tumor cell‐induced P‐selectin (Figure 6A) and PS exposure (Figure 6B) and tumor cell–platelet interaction (Figure 6C). The gene discussed is PRKCA; the disease is neoplasm.