I am glad it looks like your son will be okay. This is becoming more and more common at younger ages. I tell my friends to get a colonoscopy because you feel like a supermodel after. You can fit into your tightest pants!
Years ago my husband made two documentaries about cervical cancer and he interviewed a doctor in Germany who had discovered that the virus HPV causes cervical cancer.
He asked the doctor if he thought any other cancers were caused by a virus. The doctor told him that there was already evidence gathering that colon cancer is caused by a virus in red meat. That put my husband off red meat for good!
Best wishes to your son on his full recovery.