Cancer starts when abnormal cells grow out of control. However, it must be remembered that cancer is not one but many diseases. It can develop in any organ, and well over 100 different cancer types have been recognized to date.

In Western-type industrialized nations, cancer remains the second most common cause of death, with the most frequent cases including breast, colorectal, lung, and prostate cancer. The treatment depends on the type of cancer and the degree of its metastatic spread (stage); major treatment modalities include surgery, radiotherapy, and drug treatments, alone or in combination.

Tumor markers are molecules (mostly proteins) found in the blood or other body fluids of cancer patients. Although most tumor markers are also produced by normal cells, their production is much higher in cancers.

Tumor markers may be used as an aid to (1) detect cancer, (2) predict a patient’s response to cancer therapy, (3) evaluate a patient’s response to treatment, or (4) determine whether the cancer has returned.

More than 20 tumor markers are currently in clinical use, and many national or international medical organizations have issued guidelines recommending the use of tumor markers for certain types of cancer.