I read about mucus associated with colon and or rectal cancers. does this mucus exit the rectom or is it inside only, does it cause rectal itching?

Mucous is normal: There are glands in the rectal area that lubricate the anal canal when you pass stool. This is normal. Because colon and rectal cancers can arise from the cells that make mucin (which is the protein in mucous), colon cancers sometimes also produce mucin. Rectal itching can be from a number of causes, cancer is not the most common cause of anal itching.