Raise your hand if you’ve had a family member with cancer.

If you’ve ever wondered what that means for your own cancer risk, you’re not alone. “Cancer is a disease that touches us all in some way. Everyone has had someone in their family with cancer,” says David Lieberman, MS, CGC, genetic counselor at Penn Medicine. “People get concerned about that and ask, ‘What are chances that I or other family members will develop cancer, too?’”

Yes, cancer is due to genetic changes, but that doesn’t generally mean it’s inherited.

“We see a huge amount of confusion about this,” says Katherine Nathanson, MD, Associate Professor of Genetics at Penn Medicine. “There is an inherited variation in different genes, which can lead to cancer that runs in families.

Then, there are somatic changes, which means the genetic changes are only in the tumor, and not passed onto children.” Somatic changes—also called sporadic mutations—happen by chance, but they can also be related to lifestyle and environmental exposure. Whereas genetic changes that can lead to familial cancer—also called germline mutations—stem from an inherited risk from your parents.

So, how is cancer genetic if it's not inherited?

When most people hear the term genetic, they think of genes inherited from their biological mother and father. These genes are like instruction manuals, directing how your body should form and function.

With cancer, each tumor has this set of genes as well. Similarly, for cancers like leukemia, lymphoma, and multiple myeloma, the cells in the blood and bone marrow have this same set of genes. However, there can be a change—or mutation—in those genes, which leads to differences in the properties of the proteins encoded by the genes.

“These change are what’s driving the cancer and causing cells to proliferate and not die off,” explains David. “Cancer is an accumulation of these mutations.”

To determine which genetic mutations are driving the cancer, Penn Medicine’s Center for Personalized Diagnostics can perform a gene panel test on a sample of the tumor, blood, or bone marrow.

How do you know when cancer is inherited?

In some cancers, these genetic mutations are passed on from parents, which means they can be passed on to the next generation as well. Breast cancer, for example, is most well known among inherited cancer diseases. Mutations on the BRCA genes are often passed from parent to child, increasing the risk of various types of cancer, including breast, ovarian, prostate and pancreatic cancer.

While most breast cancer is not inherited, there are several red flags that suggest a cancer runs in the family: If family members develop cancer at an early age; when many people in the family have cancer, particularly the same type of cancer or rare cancers; and when individuals have multiple primary cancers.

These signs might prompt referral for a genetic evaluation, says Dr. Nathanson. During this evaluation, the following questions may be asked:

• Which relatives have had cancer?
• What was the cancer type?
• How aggressive was the cancer?
• When was the relative diagnosed?
• At what stage was the cancer diagnosed?

“When there’s an excess of tumor types or a pattern of tumors in the family, that could mean there’s an inherited variation,” says Dr. Nathanson.

Keep in mind that different cancer diagnoses could still indicate an inherited mutation.

“If a family has a mutation in the BRCA-1 gene, one relative might get breast cancer, but someone else might get ovarian cancer,” Dr. Nathanson explains.

Here’s another clue: “If the cancer runs in a family, you’ll often see cancers clustering among relatives,” David says. “And you’ll see it more frequently at a younger age.”

Relatives who are at risk but have not been diagnosed may be recommended to have screenings at a younger age—and more frequently—than those without the family history.

Learn about our Cancer Risk Evaluation Services