It would help if we had a clearer idea of what cancer is. Some cancers are known to be caused by viruses. Maybe someday they will have clearer distinctions between viral cancers and other cancers and that will help solve mysteries like this one.
I'm frankly surprised by this. The only thing I had ever heard of was the Japanese smoking paradox where Japanese people smoke at higher rates and have lower rates of lung cancer. How or if that relates to this, I don't know.