Genetic tests may be helpful, but understand their limitations

genetic tests
When it comes to managing the cancer risks you’re born with, you may gain new insights with the help of a blood test.

You can take lots of steps to help reduce your cancer risk. Quit smoking. Cut down on alcohol. Wear sunscreen. These and other lifestyle changes may significantly reduce your cancer risk. But when it comes to managing the cancer risks you’re born with—the ones that may be lurking in your genetic profile—the strategy requires more than changing your diet or your daily habits. It often starts with gaining new insights—by determining whether certain gene mutations have been passed on to you, with the help of a blood test.

Genetic tests look for mutations in specific genes that may indicate an increased cancer risk. "A patient can use that information to increase screening that may help to find a cancer early," says Melanie Corbman, a licensed, certified Genetic Counselor at our hospital in Philadelphia. "And there may be the option of prophylactic surgery to reduce the risk of getting cancer." In the most high-profile example, actress Angelina Jolie chose to have a prophylactic double mastectomy in 2013 after learning she carried a mutated BRCA1 gene that increased her risk for developing breast, ovarian or other cancers. Jolie's mother died at 56 of ovarian cancer. Two years later, Jolie underwent another preventative procedure, to remove her ovaries and fallopian tubes.

But as instructive as genetic tests may be, it is important to understand that they have their limitations in measuring cancer risk. For example, they cannot predict with any certainty whether you will get cancer, nor can they pinpoint the exact cancer you are mostly likely to develop. Identifying a gene mutation may only mean you have an increased cancer risk, and your risk may involve multiple cancers. Not all cancers are linked to gene mutations, either. In fact, inherited gene defects have been linked to just 5 to 10 percent of all cancers, according to the National Cancer Institute.

Still, genetic tests may be helpful in measuring risk for some key, common cancer types, including breast, colorectal, pancreatic, ovarian, prostate, thyroid and uterine. The tests typically identify inherited cancer syndromes, characterized by defective genes that are passed through generations.

Common syndromes

Some of the most common syndromes include: 

syndrome Genes Associated cancers
Hereditary breast cancer and ovarian cancer syndrome BRCA1, BRCA2 Breast, ovarian, prostate, pancreatic
Li-Fraumeni syndrome TP53 Breast, soft tissue sarcoma, bone, leukemia, brain, adrenocortical carcinoma
Cowden syndrome PTEN Breast, thyroid, endometrial
Lynch syndrome MSH2, MLH1, MSH6, PMS2, EPCAM Bowel, endometrial, ovarian, renal pelvis, pancreatic, liver, stomach, brain, breast
Familial adenomatous polyposis APC Malignant and benign bowel tumors, brain, stomach, bone, skin
Retinoblastoma RB1 Eye (retina), melanoma, and soft tissue sarcoma
Multiple endocrine neoplasia type 2 RET Thyroid (medullary), benign adrenal gland tumors
Von Hippel-Lindau syndrome VHL Kidney, multiple noncancerous tumors
Source: National Cancer Institute

Genetic tests are not for everyone. "There are some red flags for who should have a genetic test," Corbman says. You may also consider getting a genetic test if:

  • You had been diagnosed with cancer as a young adult or at an age younger than benchmarks set for specific cancers, such as under the age of 50 for breast or colon cancers.
  • Cancer has been discovered in both organs in a set of two, such as the breasts or kidneys (known as a bilateral cancer).
  • You have a strong family history of cancer, such as several relatives on one side of your family diagnosed with the same type of cancer.
  • More than one type of cancer runs in your family.
  • Another member of the family has a known gene mutation.
  • Family members were diagnosed with cancer at a young age.
  • You are of a certain ethnicity, such as African American or Ashkenazi Jewish, that may have a higher risk of mutations in genes associated with a risk for cancer.

A genetic counselor may help determine if a genetic test would be beneficial, and is typically the professional who helps interpret the test results. If you choose to get a genetic test, Corbman recommends being prepared for the wave of emotions you may experience after getting the results. "A positive result may make you feel anxious or guilt-ridden," Corbman says. "Sometimes the hardest thing to accept is that you may have passed this on to your children."