Lack of knowledge about cancer's hereditary factors.

I have a question about the chances of my sister and I getting cancer. I am 22 and my sister is 28. There are only three children in my family, the other is a boy (24) . I am told that my maternal grandmother died of uterine cancer or pancreatic cancer but it can't be confirmed because none of my family members still living was alive before she died. My maternal grandmother died of breast cancer at about 40 years old after having 8 children, 3 of which were female. One of my maternal aunts died of a brain stem tumor in her thirties after having 2 children. My other maternal aunt had throat cancer when she was in her thirties, but she is fine now. My mother died of brain cancer at 45 after having three children. One of my maternal uncles(53) as well as my sister have been to the doctors often over the past two-three years with reoccurring cysts. My sister has three and my uncle has one, both after two surgeries. They have put my sister on birth control to regulate her hormones. She has four children and now due to the hormone treatment she weighs 180 pounds at 5'1". My sister and I both used to be active but with the massive weight gain she has become..nearly completely inactive. I am unsure of what they are doing for my uncle. I am really just trying to understand if cancer is really heriditary. I have read in articles that it is but I am having a hard time understanding why my sister and I might get cancer. I have only spoken to doctors about this during my sister's operations, but what can be done to prevent this? Do the reoccuring cysts mean that my sister is "getting" cancer? I asked one doctor about this during my sister's last surgery and she explained to me that she was unsure because cancer of the brain is not hereditary even though both my aunt and my mother died of some form of it. I just really want some answers or some advice other than wait it out.

[DrNoopurMD]

Hi,

On an average about 5-10% cancers are hereditary. The most common hereditary cancers are breast cancer, ovarian cancer, prostate and colorectal cancer. As your doctor rightly told you brain cancer is not a hereditary cancer. To know the exact risk that you and your sister face, you will have to undergo genetic testing. Genetic counselors discuss family history in great detail and then calculate the risk. Since you have many family members who had cancer it is advisable that you and your sister seek genetic counseling.