A method for diagnosing a malignant proliferative disease or disorder in a subject, and/or for following up, monitoring or prognosticating the therapy of a malignant proliferative disease or disorder in a subject is disclosed. The method is based on measurement of platelet-mediated fibrinogen-like protein 2 (FGL2) activity in a sample essentially comprising platelets obtained from the subject. In accordance with the disclosed method, platelet-mediated FGL2 activity level higher than control is indicative of the presence of a malignant proliferative disease or disorder in a subject.