[krisoft]

It sounds like you are hang up on the fact that everyone "might have cancer", thus technically everyone "might have cancer"?

It depends on the context of the sentence. It is unlikely that they just sent out a one line email saying "you might have cancer" and nothing more.

If the context of the letter makes it clear that they are raising awareness about the possibility of people having cancer (such as for example listing symptoms to look out for, or general population statistics) that cannot be done "wrongly". (It might be still unduly alarming, distasteful, factually incorrect or unethical for a host of other reasons.)

If the context is that they are telling you that they have run tests on your recent lab samples, and those tests are positive for the presence of cancer. That is an entirely different animal. That can be done "wrongly" if for example they have not done lab tests or the lab tests do not indicate that you have a higher probability of having cancer.