I know a woman of about 50 that had routine colonoscopy and they found a baseball sized tumor. She had it removed and luckily it was benign. She had no symptoms at all and is fine. Last summer I saw photos of her rapelling on Facebook.
Cancer is many diseases. Damage to cellular DNA from a myriad of causes. Oncogenes are genes that regulate how cells divide when we are developing in utero and are shut off before birth.They can get reactivated bt smoking, chemicals, cosmic rays, mutations caused by the natural error rate pf DNA repair enzymes, etc. Each type of cancer needs a unique approach.