I think you should have your head checked first. If you're simply assuming that you have a stage 3 or 4 cancer because you have pain somewhere, then your thinking is very skewed.
Let's just say for a minute that you did though, yes you easily could, depending on what type of cancer it was though. Your question really can't be answered the way it was posed.
There are so many types of cancers, it's impossible to say what you would have. When I was 20 I was misdiagnosed for 3 months which allowed my testicular cancer to spread. By the time they found it, I was too far gone and they said I'd die from it. I'm now 47 and I have a completely different cancer now. A soft tissue sarcoma that statically should have killed me a few years ago. I'm still having chemo, but the outlook is pretty good as of my last scan. Being 18 years old, the chances of you having cancer are extremely low. I really don't think your pain is being caused by cancer, but you didn't really explain your pain good enough for anyone to answer your question.
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