Cancer

Cancer is a term used for diseases in which abnormal cells divide without control and are able to invade other healthy tissue.  Cancer cells spread to other parts of the body through the blood and lymph systems.  There are more than 100 different types of cancers which are named for the organ or type of cell in which they appear – e.g., lung cancer, colon cancer, breast cancer, prostate cancer, liver cancer and stomach cancer. 

Occurrence of cancer increases as people age. In the United States, men have a 1 in 2 lifetime risk of developing cancer and for women the risk is 1 in 3. Within 10 years, because of the aging population, cancer may become the leading cause of death.

The American Cancer Society (ACS) has estimated that there were over 12.3 million new cancer diagnoses worldwide and roughly 7.6 million deaths during 2007, of which nearly 40% were in developed nations.  Although the United States has reported declining cancer-related deaths for the past few years, the World Health Organization estimates that worldwide there will likely be approximately 16 million new cancer diagnoses annually by the year 2020, with roughly 10 million related deaths each year.  Over the next 20 years, the global incidence of cancer is projected to increase by 50%. 

The growing numbers of people developing and living with cancer will likely continue to increase the demand for cancer diagnostic products.  In particular, two diagnostic areas that have significant unmet need are the early detection of primary cancer and early detection of recurrence after therapy. A practical way to detect these cancers is by detecting the presence of cancer markers in blood.

Cancer Markers

Cancer markers are a group of proteins, hormones, enzymes, receptors and other cellular products that are produced in higher than normal amounts by malignant cells.  Cancer markers are usually normal cellular constituents that are present at very low levels in the blood of healthy persons.  If the substance in question is produced by the cancer, its levels will be increased in blood or other body fluids or in the tissue of origin. 

Routinely used cancer markers include AFP (the first clinically useful cancer marker, discovered by Dr. Garry. Abelev, a member of our Scientific Advisory Board), PSA and CEA (discovered by Dr. Phil. Gold, a member of our Board of Directors).

Detecting a cancer marker in higher-than-normal amounts in the body may signify the presence of a malignancy.  For some indications, the expressed amount of a particular marker can also signal the stage of the disease (i.e., how far the cancer has progressed).  For instance, a common cancer marker for liver cancer, alpha-fetoprotein (“AFP”), not only signals the potential presence of liver cancer, but can also indicate the size of the tumor.  However, it is important to note that the sensitivity of AFP as a cancer marker is only approximately 60%, meaning that roughly 40% of patients with liver cancer do not have an elevated AFP.  (Note: Sensitivity is the ability of a test to detect cancer.  If all cancer patients test positive for having cancer with a particular test, the sensitivity of that test would be 100%.  Specificity measures how well the test detects healthy individuals, i.e., whether it produces false positives, that is, falsely identifies patients as having cancer when they do not.  If a test does not return any false positives, it has 100% specificity.)

After testing for a cancer marker, further identifying the cells that express the marker may enable a definitive diagnosis.  Oncologists measure marker levels to assess a patient’s response to treatment, evaluate appropriate future treatments, and check for signs that the cancer may be recurring.  If, after treatment, marker levels have decreased from the level at diagnosis, it may indicate that the cancer is responding favorably to the treatment.  Conversely, if marker levels rise, the oncologist may consider an alternative therapy option, as the tumor is probably not responding to treatment.  Depending upon the patient and the cancer, these follow-up tests may be continued for life, occurring as frequently as every two to three months.

Currently, there is only a handful of cancer markers widely used in clinical practice. Some examples of these cancer markers are PSA for prostate cancer, CEA for colorectal, AFP for liver cancer and CA125 for ovarian cancer. While those are the main cancers they detect, these markers are not 100% organ specific: AFP can be found in some testicular cancers, CEA is also expressed in some breast cancers and lung cancers.

The main drawback of current cancer markers is their low sensitivity, i.e. the number of cancers they catch. Also, they are not very cancer-specific: for example, blood PSA is increased when the prostate size is augmented, a very common situation in older men. As a result, 2/3 of prostate biopsies resulting from an elevated PSA blood test are benign and therefore unnecessary.

This lack of cancer-specifity is not limited to cancer marker tests; it is also found in mammographies: 3/4 of breast biopsies result in benign lesions that require no further action and are, therefore, unnecessary.