Cancer Biomarkers

There has been much interest in biomarkers of cancer risk in predicting future patterns of disease, especially as cancer treatment has made such positive strides in the last few years.  A biomarker is any substance that is measured biologically and associated with an increased risk of disease.  Biomarkers can be present in the serum, or be genetic testing factors, and all are being studied acutely to find out how they can be of more use in cancer screening.

Serum biomarkers are produced by body organs or tumors and measure antigens on cell surfaces.  When detected in high amounts in blood, they can be suggestive of tumor activity.  Serum biomarkers are nonspecific for cancer and can be produced by normal organs as well.

One of these serum biomarkers in wide use is PSA.  PSA is produced by normal prostate cells in small amounts, but the higher the PSA is in the serum, the higher the correlation is toward the existence of prostate cancer.  PSA is probably the only serum biomarker currently used consistently in primary care.

There are reasons other than cancer that can cause rises in PSA.  Infections within the prostate gland (prostatitis), increased exercise with irritation of the affected area, and even vigorous physical examination by a doctor can cause a PSA rise.  Factors such as the degree of elevation, the rapidity of increase, and the fraction of free non-bound PSA (higher in benign causes) are all factored in to determine a next step.  While no treatment is ever based solely on a PSA, alterations above normal can spur further diagnostic testing to catch the disease at an early stage.

Cancer antigen 125 (CA-125) can be a biomarker of ovarian cancer risk or an indicator of malignancy, but it has low sensitivity and specificity.  Levels of this marker can be high in people who have pancreatitis, kidney or liver disease, making its accuracy as a cancer diagnostic tool very limited.  However, it can be used to follow the progress of treatment of cancer, and predict a treatment failure when levels rise despite the use of chemotherapeutic agents.  Sometimes, a combination of several tumor markers can give risk predictions in someone whose family history for the disease is quite high.

Carcinoembryonic antigen (CEA) is another biomarker that is elevated in patients with colorectal, breast, lung, or pancreatic cancer.  As a screening test, it can be elevated by many other factors than cancer; smoking for instance raises CEA levels.  Following CEA post-surgery for colon cancer however is an effective way of determining the adequacy of postoperative therapy.

While PSA is used in insurance testing to assess the risk of underlying prostate cancer, other biomarkers are not specific enough nor cost effective to use.  There are even questions with PSA, as some prostate cancer may be so slow growing as to never affect eventual mortality or be unlikely to progress.   Genetic testing is still not sophisticated nor accurate enough on which to forecast risk, and is not part of the testing required by insurers.