One of my patients has been post-operative for breast cancer for almost five years now. At that time, the patient did not have any symptoms and the liver ultrasound and CT examination did not reveal any abnormality. The patient had been very concerned about the elevated CA153 value, but since the imaging did not reveal any problems, the patient was asked to have a repeat CA153 test one month later. When the results of the repeat test came back, the CA153 value reached 50 U/ML. A full review was given again, including an MRI of the liver, which still did not reveal any abnormalities. The patient then underwent whole-body PET-CT, which revealed a 2 x 3 cm sized occupying change in the right liver. The pathology after surgical resection suggested: liver metastasis of breast cancer. the CA153 index test then dropped to normal. Two years after the patient’s liver surgery, the elevation of CA153 index appeared again, and the same ultrasound, CT and MRI still did not detect the lesion. The second PET-CT examination revealed three occupying lesions in the liver, which were treated with chemotherapy. The patient’s long-term survival depends on the early detection of his liver metastases, and the early detection should be attributed to the examination of CA153. Although this is an extreme case, it can fully illustrate the importance of tumor marker examination. Clinically, the imaging principles of ultrasound, CT and MRI are different, and often they can corroborate and complement each other in the examination. However, this patient did not find any lesion in the above mentioned examinations, and the elevation of CA153 became the only clue suggesting tumor recurrence. Tumor markers have been clinically used for more than 100 years now and are gaining more and more attention. Because the test is simple and easy to perform and inexpensive, it has a very important role in certain tumors. However, at present, due to various reasons, there are still many doctors who only pay attention to the imaging examination of tumor patients and ignore the detection of tumor markers. This is detrimental to the early detection of tumor recurrence and metastasis. Because clinically, abnormalities of tumor markers can be detected months before the imaging examination. In addition, tumor markers also play an important role in various aspects of tumor screening, judgment of treatment effect and prognosis assessment. Clinicians, especially those specializing in oncology, should have a correct and clear understanding of tumor markers.