Jimmy Carter knew this day might come.

His two sisters, brother, and father all died of the same illness: pancreatic cancer.

Now, at age 90, he has been told he also has cancer and that it has spread.

Having a strong genetic predisposition to a certain type of cancer does not guarantee that you will get it, but it does mean you should get genetic testing and take sensible preventive steps, Joy Larsen Haidle, president of the National Society of Genetic Counselors, tells Newsmax Health.

People inherit half their genes from each their parents, so this means there is a 50-50 chance of inheriting a cancer gene, said Haidle, who is the organization’s genetic cancer expert.

While Carter has not said what type of cancer he has, experts say it is likely pancreatic cancer, given his strong family history and the fact the disease was discovered in his liver, which is adjacent to the pancreas.

In a sense, Carter’s late-in-life diagnosis can be seen as a triumph by him over his genetics.

He managed to stave off cancer until he was elderly, unlike his brother Billy, who died at age 51; father James Earl, who died at 58; and sisters Gloria and Ruth, who passed at ages 63 and 54, respectively.

Jimmy’s mother, Lillian Gordy Carter, also died of cancer. She was 85 when she succumbed to breast cancer.

In his autobiography, Carter says he was only one in his family who didn’t smoke, and he says that may be why (until now) he avoided cancer.

Most cancer scientists believe in a “two-hit” theory of genetic cancer, which means that although a cancer gene is inherited, something has to happen to initiate it.

“When you inherit a cancer gene, that gene is present since conception, so something else needs to trigger it,” said Haidle. “Getting regular exercise, maintaining a healthy body weight, and not smoking can play a role in the development of cancer or delay or prevent it.”

In light of Carter’s family history, he was closely monitored through the years, getting extra scans and screenings.

Among the cancers known to have the strongest genetic links are ovarian cancer, for which 24 genes have been discovered; breast cancer, 18 genes; and colon cancer, 17 genes.

“There are genes for pancreatic cancer that we haven’t discovered yet. It’s a difficult cancer to study because it is so deadly It’s usually diagnosed at an advanced stage, and patients may pass away before research can be done,” she said.

Some people are reluctant to undergo genetic counseling for cancer because they are afraid of what they might learn, Haidle noted.

But such a process often puts minds at ease, she said. Many people think they have a family predisposition when the cancers are actually caused by other factors. In fact, heredity is thought to be responsible for only 5 to 10 percent of all cancers.

“Sometimes people are alarmed because there seems to be a lot of cancer in their family, but upon a closer look they learn that these cancers occurred due to chance, not heredity,” she added.

People have also worried that learning they have a genetic risk for cancer could endanger their health insurance or lead to job discrimination. But there are now federal and state laws that prohibit this, she noted.

The best way to determine if you need genetic cancer counseling is to make a family medical history tree, which is similar to a regular family tree, but with medical information. Your doctor can help you do this.

According to Haidle, you should consider cancer genetics counseling if you have:

• Family members diagnosed with cancer at earlier-than-expected ages, such as under age 50 for breast or colon cancer.

• Multiple relatives who developed two or more different types of cancer, such as breast and ovarian cancer, breast and colon cancer, or breast and thyroid cancer.

• Three or more family members on the same side of the family with the same type of cancer.

Others who should consider genetic counseling include men with relatives who developed male breast cancer or particularly aggressive prostate cancer, and women who have any relatives who developed ovarian cancer, Haidle said.

Genetic testing usually includes a simple blood draw which is analyzed to determine if known cancer genes are present.