cancer?

I have a major question what does the father having those bumps on his face (and they actual are cancer lumps) have to do with anything ?its not like it effects the plot in any way and in the end of the book he doesn't die so I don't see the significance of mentioning it at all and the only time they mention it is in two poems and that's on page 154 and 209. So what do you think and do you think it effects the plotand if you do how?