[ElaineM]

I am sorry about your aunt. You can be a great support to her, because you have "been there and done that".
I hope there is not a common genetic reason many family members developed cancer.
I think scientists and doctors still have much to learn about the causes of cancer. There may be other genetic reasons still unknown. Diet, lifestyle (I. E. smoking etc.) and enviroment can also contribute to the development of cancer. Sometimes there may be a combination of things that contribute to a person's cancer diagnosis.
However, scientists are also learning about "Cancer Clusters". That means that a significant number of people in an area develop the same kind of cancer. Various environmental factors may cause this. Did the people in your family who developed breast and prostrate cancer live in the same general area of the country? It might be a good time to do a little research on your family tree. In any case I wish you all good health. Take good care of yourselves.