A person's genetic predisposition, while not the sole determination of whether a person will get a certain form of cancer, does affect the odds.  For instance, those who are born with a certain mutation or defective gene have a higher likelihood of developing cancer earlier than those without the abnormality.
 
Some cancers, heredity is more of a factor than with others.  The four cancers in which heredity plays the largest role are breast cancer, ovarian cancer, prostate cancer and colorectal cancer. 
 
It's not always easy to know if you have a genetic mutation that puts you more at risk of developing cancer.  One way is to request genetic counseling.  A genetic counselor will talk with you about your family history, ask a variety of questions, and from this interview determine what your risk factor is.  Depending on what he or she decides your family history dictates, he might recommend genetic testing.
 
Genetic testing refers to the use of lab tests to get a more accurate evaluation of your chance of developing cancer based on genetics.  The type of tests will differ, depending on the type of cancer that's being investigated.  You are never required to undergo genetic testing.  This is a decision that only you, with the advice of your physician, can make.
 
With inherited ovarian and breast cancer, these two diseases are many times linked. That's because the cancers develop from the same genetic mutations--from the genes called BRCA1 and BRCA2.  These two genes control multiplication in cell and are also responsible for repairing DNA damage.  If the gene itself has been damaged or become mutated, it loses the ability to do its job correctly.
 
Here's how the defective gene is passed on to offspring.  We have two sets of 23 chromosomes in the human body.  Each of these sets contains DNA from both the father and mother. Each chromosome contains thousands of genes, each coming in pairs.  One of these pairs is the BRCA gene--half the DNA coming from the mother and half from the father.  If one of the parents' genes is mutation, it could be passed to their child during conception.
 
A simple blood test can be used to detect the presence of a mutated BRCA, and it's often recommended that those with ovarian or breast cancer have this test done; this will provide important information to the cancer patient's family.
 
Another form of cancer, this time striking only men, is prostate cancer; it has been found that six genes affect development of this form of cancer. Unfortunately at this time, there have been no tests developed to identify these particular genes.
 
The third most common cancer in the United States is colorectal cancer.  An estimated one of every 17 people will get colorectal cancer at some time in their lives.  Of these cases, five to 10 percent can be attributed at least partially to genetics.
 
Anyone who knows of a family connection with cancer should speak to their physician about this.  Your doctor can tell you if genetic counseling or testing will help you better assess your chances of developing the cancer, and steps you can take to fight it.