I had skin cancer when I was 25. Scared me. The doc cut it out, and I was fine, but as people are saying, just the word (or rather diagnosis) "cancer" is scary as hell. It easily translates in my head to "your life is over now. Sorry, that's it. You're done." But I was fine, of course. My mind can really get carried away with worry and doomsday scenarios, sometimes. The worst is when I drop into a sort of hopeless and self-pitying mode. That doesn't do a damn bit of good.
I'm assuming the doc can cut it out, and you'll be fine. Meanwhile, what I found to be helpful is prayer in whatever way you're comfortable (especially just expressing your raw feelings), talking with people about it, and letting yourself feel your feelings. Re. the latter, people always say to "think positive," and although that has some value, trying too hard with that can backfire by creating stress, because you're trying to repress legitimate feelings (fear, anger, hurt, whatever). It's better to treat yourself with as much kindness, support, and acceptance as you can.
Sending you love.