Platelet-activating factor (PAF) is a lipid mediator that is well-known for its ability to cause platelet aggregation, inflammation, and allergic response at very low concentrations (approaching picomolar). This potent signaling compound is secreted from tumors, as well as from cells derived from carcinomas.

Platelet disorder refers to the decreased number of platelets (thrombocytopenia) or the dysfunction of platelets (platelet insufficiency), which can cause the abnormal thromboembolism and bleeding. Thrombocytopenia, which means that the platelet concentration is below the normal range (140,000 to 400,000 /μL), may be due to the insufficient platelet production, the platelet retention by the spleen, increased platelet use, destruction or dilution (Table 133-1). Regardless of the cause of it, thrombocytopenia can cause a typical bleeding including multiple ecchymosis which most commonly occurs in the lower leg, the small scattered ecchymosis in the sites of minor trauma, mucosal bleeding (epistaxis, gastrointestinal bleeding, urinary tract bleeding and colporrhagia) and postoperative massive hemorrhage. Gastrointestinal bleeding and internal massive hemorrhage in the central nervous system can be life-threatening. However, thrombocytopenia does not occur as a secondary to coagulopathy.