A stats question -- about survival analysis and censoring

Dear UseRs,

Suppose I have data regarding smoking habits of a prospective cohort and wish
to determine the risk ratio of colorectal cancer in the smokers compared to
the non-smokers.  What do I do at the end of the study with people who die
of heart disease? Can I just censor them exactly the same as people who become
uncontactable or who die in a plane crash?  If not, why not?

I'm thinking that heart disease isn't independent of smoking even though
a death from heart disease is probably uninformative about colorectal
cancer risk. Hence
I suspect simply censoring these deaths will introduce a bias, but I don't know
how to correct for it.

Many thanks,

Geoff Russell -- an interested student