Please try not to worry too much. Both my middle aged sons have had skin cancer of the worst kind (melanomas) One had one appear on his back and he had never exposed that area to the sun, so tell me how that is? The other one had one on his upper leg, again never exposed to the sun?
I am inclined to believe that there is probably more connection to a genetic pre disposition than is commonly realised. I have a brother who has also had a melanoma removed some years back, but in his case it was on his face and he had extensive sun exposure in his history.
I am very happy to report that the youngest had his diagnosed and operated on and treated nearly 15 years ago, and despite a very grim prognosis has not had a single problem since. The oldest one had his operated on and treated 2 years ago, he is still checked regularly by the hospital but shows no signs of any further problems.
What I am trying to say here is - please think positive, these days the ops to remove the melanoma and the ongoing treatment has a very high success rate. Positivity is also a very useful healing tool IMO.