Does cancer that runs in families always mean a syndrome?

No. Cancer can appear to run in a family for reasons that have nothing to do with an inherited syndrome.

The National Cancer Institute points to several. Common cancers, such as prostate cancer, can appear in several relatives simply by chance. Relatives often share habits and environments — such as tobacco use or air pollution — that can lead to similar cancers. And a family may share a combination of many genetic variants that each add only a tiny bit of risk, rather than one strong syndrome.

So a family history of cancer is a clue worth exploring, not proof of a syndrome. Patterns such as cancer at young ages, several relatives with the same cancer, or rare cancers make a syndrome more likely. A genetic counselor can review the pattern and explain whether testing might help.