Tumor markers in cancer prevention and detection

Tumor markers are a major part of the secondary prevention (detection) efforts. There are major logistic and economic constraints which could be overcome if a simple laboratory test could be devised that would (based on a sample of blood or urine) indicate the presence of cancer--with a high degree of specificity and sensitivity--before there are metastases. Hence, it could serve as an acceptable screening test for initiating definitive diagnostic procedures with a goal of making an "early diagnosis:" that is, a diagnosis before metastasis has occurred, and when simple removal of the tumor would result in normal survival characteristics for a population of patients. No such test exists, although extensive efforts have been made and a number of tumor markers have been described and tested. To date, no combination of markers has been found that meets the criteria set. Tumor markers have principally been used to monitor therapy, i.e., predict outcome or signal a recurrence. Most of the markers described fall into the classes of oncofetal antigens (CEA), (alpha-fetoprotein)-hormonal products (HCG, ACTH), enzymes, and the polyamines. There are several recent books devoted to tumor markers. The major features will be reviewed.