Apparently he had that cancer from both sides of the family. It sucks but what can you do. I don't want to be a downer, but if your spouse has the same history of a deadly malady from her side, you should think twice about having kids. Combining the same gene combines twice can fuck you up, that's why incest is illegal. By marrying someone with a different genetic makeup, you minimize/dilute these kind of things. But once in a while like TotalBiscuit's family's case, your medical background can match with strangers as well.
At the very least you should pay MASSIVE attention to a sickness, if it exists in both sides of the family.