Who should consider genetic testing for cancer?

Is there a significant history of colon cancer in your family? Was a relative diagnosed with colon cancer at a young age? If so, you may want to ask your doctor about genetic counseling.

Like all cancers, genetics can play a critical role in the development and progression of colorectal cancer, which includes cancer of the colon and rectum. About 5 to 10 percent of all colorectal cancers are caused by gene mutations inherited through generations.

The likelihood of having one of these inherited mutations is relatively small, but your risk of developing colorectal cancer is significantly higher if you carry one of these genes, says Candy Nehlsen Hofman, a genetic counselor at Sharp HealthCare.

Genetic counselors help patients and family members understand the likelihood that they have an inherited mutation, the genetic tests that may be useful to find a mutation, and what the test results mean. This is true for patients already diagnosed with colorectal cancer and for people with a family history of the disease.

“There are hundreds of genetic tests on the market — with new ones being advertised every day,” Nehlsen Hofman says. “A genetic counselor is trained to help patients navigate which ones may be useful, and they can put results in context for you and your loved ones.”

Types of inherited syndromes
A gene is a segment of DNA that contains instructions for cells to make proteins, which have varying jobs within a cell. Many of these proteins are involved in the response to — and repair of — DNA damage. Others help control how a cell grows and divides.

A gene mutation changes these instructions, affecting the cell’s ability to make proteins. Without these proteins, it becomes more difficult for a cell to correct DNA damage or control how the cell grows — increasing the likelihood that cancer will occur. Because people get half of their genes from their mother and half from their father, a parent who carries a mutation can pass it to their child.

Several gene mutations related to colorectal cancer have been identified. Lynch syndrome is the most common of these, accounting for 3 percent of all colon cancers. People with this condition face a very high risk of developing colorectal cancer — up to 82 percent. It is also associated with other cancers, including endometrial, ovarian, stomach, kidney, pancreatic, brain or skin cancers.

Lynch syndrome is typically found in families where at least three family members in two generations have been diagnosed with colorectal cancer or the other cancers associated with the syndrome.

Other inherited conditions — including familial adenomatous polyposis (FAP) and MYH-associated polyposis (MAP) — can cause numerous polyps (benign growths) to develop in a person’s colon, usually starting at a young age. If untreated, these conditions usually lead to colorectal cancer, typically before age 40.

Who should seek genetic counseling
You may want to consider genetic counseling if:

• You were diagnosed with colorectal cancer in the past, especially if diagnosed before age 50

• At least one family member was diagnosed with colorectal cancer before age 50

• You have had numerous colon polyps removed, or at least one family member had numerous colon polyps

• Multiple family members have had colorectal cancer, regardless of age

Testing and results
Testing is usually performed on a sample of saliva or blood. A positive result could mean a genetic mutation related to colorectal cancer was detected. With guidance from a genetic counselor and other medical professionals, this information can help you make choices related to preventive care, lifestyle changes and family planning.

Unfortunately, a “negative” result doesn’t necessarily mean you are free from inherited cancer gene mutations, Nehlsen Hofman says. The discovery of genetic syndromes connected to colon cancer is relatively new, and there may be syndromes that cannot yet be detected.

Nehlsen Hofman recommends that you check in with your genetic counselor every few years to see if new testing is recommended.