Blood tests are used to detect cancer markers, which are also called tumor markers and biomarkers, in the blood, according to the American Society of Clinical Oncology. Tumor markers are substances often produced by cancer cells, although healthy cells can also produce them.
While not recommended as a sole diagnostic tool, when utilized in conjunction with other diagnostic methods, tumor markers are useful for detecting the presence of cancer. Tumor markers are commonly used for screening high-risk individuals for particular types of cancer, since tumor markers may, in some cases, show up in the blood prior to any symptoms being experienced, notes the American Society of Clinical Oncology.
In addition, tumor marker tests can help confirm a diagnosis of cancer when used with other types of diagnostic testing; they can also steer the course of treatment. For example, doctors may use a tumor marker test to decide whether to add therapies like immunotherapy or chemotherapy to the treatment plan or determine if the therapies are working, states the American Society of Clinical Oncology. As of 2015, tumor marker tests are used to look for a range of cancers. For example, the human epidermal growth factor receptor 2 test is useful in screening for breast cancer, while the prostate-specific antigen tumor marker test is used for screening prostate cancer.