The normal value of thymidine kinase in serum is 1.5-3.5 U/L. If the level of thymidine kinase reaches 4 U/L or more, it indicates the possibility of cellular carcinogenesis, or suggests the possibility of cancer existence. Thymidine kinase is a cell proliferation marker that can sharply capture the abnormal cell proliferation that is occurring in the body and is particularly suitable for precancerous condition monitoring, which can effectively indicate the risk of precancerous lesions and is a new cancer prevention tool. If thymidine kinase is mildly elevated, less than 4 U/L, it is of little significance and the patient may be rechecked again in three months. If the level of thymidine kinase on recheck is higher than 6.4 U/L and the patient has symptoms such as fatigue, wasting and pain, further exclusion by X-ray, ultrasound, CT and MRI is feasible. In conclusion, thymidine kinase is a kind of indication, and a positive result does not necessarily mean cancer or tumor, so other related tests should be done to make a comprehensive analysis before making a judgment.