A couple anecdotes:
A dear family member of mine had cancer which was successfully treated. Then, a year or two later, she came down with cancer in another part of her body which ultimately killed her.
A friend of a friend had a parotid tumor which was successfully removed and ruled benign. Then a year later she had ovarian cancer which she is currently fighting.
My common sense is telling me that these pairs of cancers are likely to be related. Especially for the second person who is just 35 years old.
My question is this: Do cancers tend to correlate in this manner? If so, is there an accepted explanation? For example, it occurs to me that operating on one cancer might release diseased cells into other parts of the body. Or perhaps chemo-therapy is itself carcinogenic. Or perhaps a lot of cancers are partially caused by a general immune system failure which opens the door to cancers everywhere in the body.
What’s the straight dope?