Abstract: A method for detecting cancer is disclosed. The method includes the steps of: (1) obtaining a test sample of body fluid from a subject; (2) measuring a calsyntenin-1 (CLSTN-1) level in the test sample of body fluid in vitro; and determining if the CLSTN-1 level in the test sample of body fluid is significantly higher than a normal CLSTN-1 level in a sample of body fluid from a healthy population of the same species as the subject, and if yes, indicating that the subject under test has cancer. Methods for monitoring therapeutic efficacy of a therapy or a medicament for treating a cancer patient and for identifying efficacy of a medicament in treatment of cancer are disclosed, and a kit for use in the aforesaid methods is also provided.