Cancer markers and tumor markers are the same thing. These markers are substances found in the blood, urine or other body fluids, and their levels indicate the presence of certain types of cancer, according to the National Cancer Institute. However, there are also noncancerous conditions that can affect these markers; therefore, doctors perform additional testing, such as biopsies, prior to making a diagnosis.
Tumor markers are a useful tool in the diagnosis and treatment of some cancers, explains the National Cancer Institute. Their presence or elevation indicate a need for further testing to confirm or rule out a particular form of cancer, and they help physicians to plan treatment. Additionally, taking further measurements during treatment helps determine how the cancer is responding to therapy and allows the doctor to adjust treatment accordingly.
As useful as tumor marker testing is in diagnosis, its limitations prevent it from being completely reliable as a screening tool, notes the National Cancer Institute. Some tumor markers can be present even in the absence of cancer, and not all patients with cancer have a corresponding change in their tumor markers. Moreover, scientists have not yet identified tumor markers for all types of cancer, as of 2015.