I ask because my family got cancer all around the same time. It goes like this-my dad's best friend got prostate cancer and died of it. Around the same time my mum got cancer too and had treatment for it. The next year my grandad got cancer and sadly died. 2 years after this we found out my dad had cancer, but with it being prostate cancer, it is very conceivable that he first got it around the same time as my mum and grandad-the same time as his best friend losing his battle with it. Before this no one in our family or their friends had cancer. They were all very healthy people. I guess my theory is that my dad caught it from his friend originally, and passed it onto my mother who then passed it onto my grandad. Maybe their immune systems were down at the time which is why they "caught" it and my grandmother didn't.
I have also noticed in news stories there is a correlation between families getting diagnosed at the same time (I seem to remember one gentleman saying he had lost both his wife and daughter to lung cancer in a very short space of time-his daughter was very young so it seemed odd). This all got me thinking. Before anyone says cancer is 100% not contagious, we don't know what causes cancer yet so I'm not sure how doctors can say for a fact that it isn't in humans. Secondly, contagious cancer occurs in Tasmanian devils-this has been proven, so if this can happen in those creatures I don't see why it can't happen in humans. Has anyone else noticed such correlations in their family/friends?