Why is cancer considered genetic?

I am wondering, a lot of times I read about cancer being hereditary/genetic. Does anyone have any information or a link on why? What research is this based on?





If the only reason scientists think so is because it is often prevalent in certain families, couldn't it also be that it is contagious/caused by a microbe that spreads in co-habiting people? It would be as valid an explanation as saying it is hereditary. Is it being masked as genetic for political correctness because so many people have it?





Please don't waste my and other people's time if you don't know what you are talking about, I'm looking for some real info.

Why is cancer considered genetic?
Ok I hope this is not a waste of your time. Not all cancers are genetic. Some people have the genetic marker for some cancers or other diseases. The occurance of these markers increases if a parent or grandparent had the disease or a marker for it. It is like a lottery, the more decendents that had the disease the more likely you are to get it. A larger part of cancers depend on a Myriad of other factors though. -Risk factors.


Here is a link for you.


http://www.cancer.gov/cancerinformation
Reply:80% of cancer is environmental 20% is heredity. Families tend to use the same products that can cause cancer without realizing it.
Reply:Cancer is considered hereditary as it involves cell mutation through mitosis and meiosis. DNA exists within cells which could lead to the explanation for it being hereditary.


It cannot be prevalent in certain families due to it being contagious as if that were the case, we would have an epidemic of Cancer - this would not only pass on in family members but to anyone else that had been in contact with this person or the area.


Some Cancers are influenced by environmental factors such as lung cancer, but individuals can have an increased probability of diagnosis if they have the hereditary lines.