As far as I know this is a very slow growing cancer and is rare. Even in the worst case most tumors are cured with a simple operation.
It is VERY unlikely your symptoms are being caused by this form of cancer, most cases occur in people over the age of 60, and I will state again this is a RARE cancer and you are VERY unlikely to have it.
The stomach pain is much more likely to be being caused by:
A stomach ulcer with or without a bug called H Pylori, the bug makes the ulcer not heal and can be treated with antibiotics
IBS - IBS goes hand in hand with anxiety type symptoms and it can cause all kinds of abdominal pains
A parasite such as round or thread worm, you will notice these wiggling in your stool (poo) if you have them, they are easy to treat.
NSAIDS like ibuprofen can irritate the stomach, causing cramps and ulcers
A colon polyp - benign growth in the colon which can very slowly turn to cancer over YEARS and can be removed simply during colonoscopy.
There are all kinds of things which can cause stomach pain, your doctor will know more once you have had the scopes done. You are doing the right thing having them done. I know it's scary but hang in there and it will all be sorted very soon.