Blood tests for cancer effects lack sensitivity and specificity and cannot be used as a basis for a definitive diagnosis. Blood testing for cancer is a humoral tumor marker test, which refers to substances produced or secreted by tumor cells, or released as part of the tumor cell structure, or produced by the host in response to a neoplastic reaction in the body and entering the bloodstream. Traditional tumor markers include carcinoembryonic antigen and alpha-fetoprotein. The advantages of blood testing for cancer lie in the convenience of retaining the specimen, easy operation, and fast reporting, etc. However, its effect lacks sensitivity and specificity, and cannot be used as the basis for confirming the diagnosis. It is mainly used for early screening of tumors, prognosis judgment and efficacy testing. If there is a need for blood test for cancer, it is recommended to go to regular hospitals to avoid delaying the condition.