Need advice.....

I feel like my breath has been taken from me so trying to get more information to know how to move forward. My birth mother died in childbirth with me and was adopted so we don't have any information on her side. On my father's side, I have an aunt who had breast cancer in her 40's, another aunt who died of Ovarian cancer that spread to the colon and stomach last year. Exactly three weeks later my Dad died of throat cancer that had spread to the lungs, brain and spine. Now....my 52 year old older sister has had an abnormal mammogram screening and went today fora compression scan. We are all so very scared and I am not sure whether this is "coincidence" or should I have testing. I am 40 years old with three very young children and would like to be proactive without letting this all overwhelm me at the same time. 

When speaking with family last night we learned that my paternal grandmother had died of "stomach & woman" cancer at a very young age (in her 30's). This was in the late 1940's.....