I say don't mess around with any kind of bump or spot that has suspicious growth, shape or coloring. My brother died in March from melanoma that started with a little mole on his lower back. It is wicked stuff that they don't know how to stop.
However, I don't think widespread itching (like all over your arms) is a common symptom of cancer. I had the same experience last summer - my arms itched like crazy and had little bumps - after every sun exposure. I thought I had developed some kind of allergy to the sun. It turned out to be because I was taking a medication and increased sun sensitivity was one of the side effects.