In the MEGA study, Blom et al. demonstrated that screening for FVL and the prothrombin 20210A gene mutation in cancer patients, assuming that subsequent prophylactic anticoagulant therapy would be effective for 80% of them, would prevent annually only 7 to 27 venous thrombotic events per 10,000 cancer patients screened [5]. The gene discussed is F2; the disease is cancer.