His wife has inoperable but treatable cancer but he is going to continue his campaign:

“The campaign goes on. The campaign goes on strongly,” Edwards told reporters, his wife by his side.
[…]
Mrs. Edwards, 57, was first diagnosed with cancer in the final weeks of the 2004 campaign. The day after Democratic presidential nominee
John Kerry and Edwards, his running mate, conceded the election to George W. Bush, Edwards announced that his wife had invasive ductal cancer, the most common type of breast cancer, and would undergo treatment.
Mrs. Edwards underwent several months of radiation and chemotherapy for the lump in her breast. Her husband’s campaign has said she had recovered from the illness.

My brother-in-law has inoperable cancer and is still living years after his diagnosis so she may still have some time (though, it’s stage four which is pretty advanced). But it will take it’s toll and I have to think that they may be changing their mind as she goes through treatment. We should keep her in our prays because it’s not easy to going through treatment and to have do campaign appearances on top of it seems impossible to me. Though, I agree with them, it’s probably better not to sit around feeling sorry for yourself but to get out there and remain active as long as you can.
When I heard of the press conference and that her cancer had returned, I thought about what I would do if I were her. I would tell me husband that I want him to continue to pursue the presidency. He obviously wants to be president and this may be his last opportunity to run. I wouldn’t want to be the reason that he didn’t obtain something that he has been working years to obtain. To run and lose is one thing but to be able to run again and then have to drop out would seem cruel to me. I would find it very hard not to push for him to continue until it was evident that he had not way of winning.