A method of diagnosing a cancer or a pre-malignant lesion is disclosed. The method comprising determining a level of expression of CD24 on leukocytes comprised in a biological sample of a subject, wherein a level of CD24 on small leukocytes and not on large leukocytes above a predetermined threshold is indicative of the cancer or the pre-malignant lesion. A method of monitoring efficacy of cancer therapy and a kit for diagnosing a cancer or a pre-malignant lesion are also disclosed.