The Potential Role of Platelets in the Progression of Ovarian Cancer

Background: Epithelial ovarian cancer (EOC) generally presents with non-specific symptoms and is diagnosed at an advanced stage. Malignant cells spread from the ovaries, along the peritoneal cavity, and formation of ascites in patients is common. Paraneoplastic thrombocytosis is associated with adverse prognosis in various solid tumors, and in EOC it is associated with advanced disease and shortened survival. If platelets are present and active in the ascites of patients with EOC, it is possible that they play a role in the progression of the disease. Research goal: Assess evidence of platelet migration and activation in the ascites of patients with EOC. Materials and methods: Patient samples consisted of plasma (n=47) and ascites (n=26) samples. Plasma samples from healthy donors (n=54) were used as controls. Hemoglobin levels were measured in ascites samples to determine which samples had blood contamination, as platelets in those samples would not represent migration only. Western blots were performed to acquire a qualitative view (full length and cleaved form) of GPIb, a platelet specific membrane protein, in patient samples. In order to get a quantitative view of GPIb in ascites samples, and thus an estimate of platelet mass, a method for GPIb ELISA was put into development. Platelet activation was determined by measuring PF4 levels with an ELISA assay, as PF4 is a cytokine specific for platelets and is released from alpha granules following activation. Results: The median hemoglobin level in ascites samples was 0.4% of the median hemoglobin level in plasma, suggesting negligible blood contamination in most samples. Western blot showed GPIb protein present in plasma and ascites of EOC patients. Development of an ELISA method for GPIb is still in progress. PF4 was present in plasma and ascites of EOC patients as well as healthy control plasmas. Discussion: The presence of GPIb indicates that platelets are present in malignant ascites of EOC patients. Only ascites samples that had negligible hemoglobin levels were used for analysis which suggests that the presence of platelets was due to migration into the ascites, rather than blood contamination, although further confirmation is needed. PF4 levels also suggest that platelets are activated in malignant ascites of EOC patients. These results support our hypothesis that platelets are present and active in the tumor microenvironment of EOC, the peritoneum. Based upon evidence of platelet interaction with cancer cells, platelets may influence the progression of EOC in the peritoneum. To what extent is a question that still needs to be answered. Our hope is that further research into the contribution of platelets on the progression of EOC might lead to new therapeutic targets against mechanistic EOC pathways that involve platelets and platelet activation, or in fact against platelets themselves