I have had a spot on my forearm for just about as long as I can remember (sometimes they are called age spots or coffee marks). This mark was not raised or "discolored", so I never gave it much thought. Anyway about two months ago I noticed that this mark had changed shape. I went to my doctor who sent me to a dermatologist. He took a scraping saying it was probably nothing. Two days later he called back and said get in here NOW! He said it was a "regressive" melanoma. This means the melanoma was breaking down and casting off cancerous cells. I went back in the next day and he remove a diamond shaped piece of skin 3"x"2" and about 1/8 deep (I now have a scar that looks like a shark bite). They sent the sample to a specialist in Columbia hospital in NYC. He called me back later and said I was one lucky man. The cancerous cells hadn't left the local area. I had literally caught it in the nick of time. He said that if I had even waited a week, I would definately be going through radiation/chemo now, with a 50/50 chance of survival. Now I have to go back every 3 months for a full body scan, forever. There's no telling how or where I got it, though I am outdoors a lot, and I never wore sunblock. I also don't have a history of this in my family. Now I treat the sun as an enemy that I must defend against. Oh yeah, I'm 59 years old.
So listen to what Tigger29 says. If you see something that doesn't look right, get it checked!!!