Summarize:

Some forms of cancer, such as breast cancer, ovarian cancer, and certain hereditary forms of colon cancer, are known to run in families and to be directly related to genes. If you have had a family member with cancer, ask your doctor if there is a potential genetic basis that can be tested for. If there is, having yourself tested can provide you with valuable information. You will either not have inherited the gene from your affected parent (meaning that your risk of cancer is the same as for the general population), or you will have inherited it (which puts you at an increased risk based on your genes).  For breast and ovarian cancer, mutations to the BRCA gene can run in families and may be tested for. For certain forms of hereditary colon cancer such as Lynch Syndrome (also known as HNPCC), genetic testing can also be performed. If you have had cancer in the past that was cured (or is in remission), you can ask your doctor about tumor marker testing which tests for the presence of any recurrence of your previous cancer. Examples of tumor markers include Ca 19-9 for pancreatic cancer, Ca-125 for ovarian cancer, and PSA for prostate cancer.. Many people worry about the exact numerical measurements of their tumor markers. However, this sort of worry is futile because the number itself means nothing (it is highly variable among different individuals). It is the progression of the number over time (with serial measurements) that provides your doctor with valuable information, and gives notice of a potential recurrence of your cancer.  If your tumor marker numbers have been steadily climbing, this is an indication that you may be having a recurrence. If, on the other hand, during the course of cancer treatments your tumor marker numbers drop, this is an excellent sign that the treatments are effective. Speak to your doctor for further information on how to interpret your tumor marker values as a means to test for cancer.
Ask about genetic testing if you have a family history of cancer. Prevent a recurrence of cancer by monitoring tumor markers. Understand that it is the progression of tumor markers over time that matters.