What is a hereditary cancer syndrome?

A hereditary cancer syndrome, also called a family cancer syndrome, is a rare inherited condition in which family members have a higher-than-average risk of a certain type or types of cancer. According to the National Cancer Institute, it is caused by inherited changes in certain cancer-related genes.

With some syndromes, cancers tend to appear at young ages. Some come with other health problems that are not cancer. Examples of these syndromes include:

• Hereditary breast and ovarian cancer, linked to the BRCA1 and BRCA2 genes
• Lynch syndrome
• Familial adenomatous polyposis, or FAP, caused by changes in the APC gene

Why a single inherited change matters so much

Cancer does not come from one broken gene. It builds up. DNA damage collects in a cell over years.

Someone born with an inherited variant starts with one of those changes already in place. It is in every cell, from birth. That cell has less distance left to travel.

That is the whole mechanism. Inheriting a syndrome raises risk but does not guarantee cancer — a person needs fewer additional DNA changes for a cell to become cancerous, but may never develop them.

It also explains the pattern these syndromes make. Cancers show up earlier than usual. Sometimes in more than one organ. Sometimes on both sides of a pair, such as both breasts or both kidneys.

How common are they

Less common than people assume. NCI says about 5% to 10% of all cancers are thought to come from harmful gene changes passed down from a parent. Up to 10 percent of all cancers may be linked to inherited changes.

That leaves most cancers to a mix of aging, exposures, and chance.

Signs that point toward a syndrome

NCI lists features that make testing worth discussing:

• Cancer diagnosed at an unusually young age, such as colon cancer before 50
• Several different cancers in the same person
• Several relatives with the same type of cancer
• Cancer in both organs of a pair, such as both kidneys or both breasts
• A rare cancer type, male breast cancer being the classic example
• Certain birth defects known to travel with inherited cancer syndromes
• Belonging to an ancestry group with a higher rate of a specific syndrome

One of these is worth mentioning to your doctor. Two or three in the same family tree is a strong reason to ask for a referral.

What changes if you have one

A confirmed syndrome does not just explain the past. It changes the plan.

Screening usually starts earlier and happens more often. It is aimed at the cancers that syndrome tends to cause. Medicines that lower risk may become an option. So may surgery to remove an at-risk organ. The finding can also shape treatment if cancer does develop. And it tells your relatives something about themselves, because siblings and children may carry the same variant.

Where to start

Ask for a referral to a genetic counselor rather than ordering a test on your own. NCI says counseling covers several things:

• How likely an inherited risk is in your family
• Whether testing makes sense for you
• What a result would, and would not, tell you
• The emotional side of knowing
• The chance of passing a variant to your children
• What screening or risk reduction would follow

Before that visit, write down who in your family had cancer. Note the type and the age at diagnosis, on both sides. That list is the raw material for the whole assessment.