The Seattle Times today points out that Washington State ranks fifth in the country for Melanoma (skin cancer), right up there with other northern long-winter places like Rhode Island and Vermont. Meanwhile, the sunniest states like Arizona and Florida have the lowest rates (according to the CDC).
Look at the PDF map of skin cancer rates in Washington State. If I changed the title of the graph to "Rainiest places in Washington", you wouldn't know the difference: there's an almost direct correlation. Eastern Washington (Yakima, Kititas, Walla Walla -- all those sunny places in the "rain shadow") have the lowest rates while Western Washington (especially the rain forest areas of Jefferson and the Olympic Peninsula) have the highest rates.
By the way, you can get all the local cancer data you want from the Washington State Cancer Registry. Someday when I get more time, it would be fun to pull the data and compare it to rainfall and other variables. For example: King County males have an incidence of 52 cases per 100,000 (females are 44).
I'm no expert, but the standard explanation seems completely backwards to me. "People in northern or rainy climates forget to put on enough sunscreen, so they get burned more often--hence the higher cancer rates"? Huh? That sounds like a classic example of a "Just So" story -- data that contradicts your central thesis (sunshine causes cancer) becomes a reason to dig a deeper hole in absurd explanations rather than a chance to rethink your assumptions.
I wonder if anyone has compared things like sunscreen sales or usage by state and location. Again, I have no idea about the medical research on this, but it seems to me that somebody might want to consider that it's the lack of sunshine that is the problem here.