It is significant because cancer is much more detectable today than in 1956-80, both because of better tests and more testing being conducted. In that earlier era, if you knew you had cancer, it was likely because it was already bad.

I also expect that of the 39.2% of the population, the cancer is diagnosed much later in life than it was for the 91 movie crew members, I doubt 41% of the crew was over 50 in 1956.