Strangely enough, my mother died of cancer, too. Actually, from complications. Multiple Myeloma. "It's not the cancer that will kill you, it's your comprimised immune system from the Chemo and the cancer."
Sure enough, one more awful infection did her in.
I think the thing that sucked wa that a couple months after they diagnosed her with the cancer they found she needed a bypass. In the end she went through that painful excerise for the privelege of not having a fatal heart attack and lingering on for a few months of infections she couldn't fight and such.