I've watched a few Ray Comfort videos so I'm not an apologist for him, but I went out searching for this information and what I found is a lot of atheist and secular material claiming Ray Comfort said these things. I find that suspect.
So have you read these books, because
More Than Just Comfort: An Answer to Cancer was supposedly written (or spoken, or recorded) in 1979 and nothing shows up on Amazon, Google book list, etc. about it. I even found an
atheist group on Reddit admitting to this and also pointing out that Ray said the quote was taken out of context and that he explained that he was dealing with people who believed they received cancer from God as a punishment and that logically if they believed that then they shouldn't seek treatment until God finished teaching these people His lesson.
Nobody can provide an ISBN number for the book to verify if this is quote mined, which I suspect it is. When
I found a list of his books on Rationalwiki, they don't list an ISBN number for
More than Just Comfort, neither do they list
Cults, Sects, and Questions as one of his published books, have you read that? Nor is the latter listed on Amazon, Google Book lists, etc.
This doesn't mean he didn't write the books. He could have and they're out of print, but it just makes it more suspicious that these quotes are only on atheist, secular sites, and anti-Christian sites.
I found a short sermon by him titled
More than Just Comfort on Soundcloud, where he shares his testimony and gives a sermon. But it's dated two years ago, not late 70's. Granted it could've been recently uploaded two years ago and is a recording from late 70's. Still, listening to it, skimming really, I heard nothing of the quote mentioned.
Even so, the man was 30 years old in 1979, he was born in 1949. Without any information on when he gave his life to the Lord, I can't say for certain, but we all start off somewhere theologically. Some of the things I thought 20 years ago theologically speaking, I realize now were a bit foolish at the time.
Trying to hold something against him from over 40 years ago without seeing if he actually said this, if you haven't read the books, or if his views haven't changed is a bit unfair to Ray and where he may stand on the issue now.