We reported three patients with an abnormal elevation of serum CA72-4 levels when taking GLSP, which is commonly used as a dietary supplement for cancer patients across the globe. Furthermore, the results were not due to the apparent analytical interference. In case 1 and case 2, excessive examinations were carried out because of a lack of timely communication with patients when the abnormal elevation of CA724 was found. In contrast, the lesson from these two cases made us communicate with the patient in a timely manner in Case 3, avoiding unnecessary examinations when the same situation happened. Therefore, it is necessary to communicate with patients in a timely manner once an abnormal elevation of serum CA72-4 is found.