Are all polylps found necessarily cancerous when you get a colonoscope?

No. Many polyps that present during this test are not cancerous, but if left in the colon, can develop into cancer. Tubular and villous adenomas can develop into cancer. Patients with familial polyposis syndromes can have many polyps throughout their colon, which makes malignancy almost certain. Sometimes the entire colon is removed to prevent it.
Polyps and cancer. Good grief, no. Lots of people have polyps when they get scoped, but they are not cancer. Some polyps can become cancer over time, that's why we remove them. And you know the worst part of the scope is the prep!