How family history affects cancer risk is an extremely complex topic. While you would think that a history of any cancer in the family would increase risk, it isn't so simple. Some common cancers – like breast and prostate – are seen in many families, but do not necessarily increase risk in that family, particularly if the person was older at the time of diagnosis.
For example, my 89-year-old grandmother was diagnosed with breast cancer. This does not affect my risk much because her cancer developed at a late age, however if my mother was diagnosed at age 45, my risk is affected, as this young age at diagnosis is more likely to be hereditary (though not necessarily). In another example, my brother, a lifetime smoker, is diagnosed with bladder cancer. Even though he is my brother, since I am a never smoker with no exposure to secondhand smoke, his diagnosis does not affect my risk because it was related to his smoking history.
You can see there is no "one size fits all" explanation for risk associated with family history. It is very important that you tell your healthcare providers about any family history of cancer- no matter how little you know about it. There are a few things that can be red flags for inherited genetic mutations, and that may warrant a discussion with your healthcare provider and consideration of genetic counseling and testing. These include: family members with cancer diagnosed before age 50 or multiple cancers, more than 1 family member with the same cancer and cancer in several generations of the family. Learn more about genetic counseling and testing and finding a counselor in your area. Use My Family Health Portrait to create a family health history.
Find out more about your cancer risk related to your family history by completing OncoLink's What's My Risk? assessment.