It's a very good question and a very astute observation. It really has to do with the fact that many different genes need to be altered by their contact with whatever it is in the environment that causes cancer in the first place. It's seldom that any single gene defect is involved in cancer. People think that it takes at least six to eight genes, but it is probably many more. They must all be altered together in the same cell before you get the change in behaviour that we would call cancer. The chance of getting all these changes at the same time in one cell is actually very low, but it increases with age.

There are some families that have a very strong history of cancer, but these are mercifully very rare. The majority of cancers are sporadic. There are probably some influences that can give you a slight increase of cancer risk, but inherited cancers themselves are actually very rare.

(Kat) If cancer is hereditary, it tends to be the same type of cancer or a group of similar cancers. (Andrew) Breast cancer in families is a known phenomenon. If the same cancer turns up in close relatives, there are some tests that can be done to find out who is most at risk. I think in your case, the cancers don't fall into any pattern that I can recognise as being inherited. The difficulty with sorting all this out is that people who share the same environment sometimes share exposure to the same carcinogens. (Fran) Cancer is such a common disease now that about 1 in 3 people will experience cancer at some time in their lifetime. Overall, the odds experienced by your family are not as extreme as they may seem.

That's a very good question and I am sorry to hear about your arthritis and cancer. I don't think they are connected. The thing about cancers that are caused by inflammation is that they tend to occur in the sites where the inflammation occurs. For example, people that have inflammatory disease of the bowel tend to have an increased instance of bowel cancer. Your breast cancer is probably an independent event. There is no evidence that I know of that that shows people with rheumatoid arthritis having an increased risk of breast cancer.