Most tumors and other neoplastic growths in the body are epithelial in origin.

• The term neoplasia = 'new growth', whereas the term 'tumor' means swelling or enlargement.

Most often neoplastic growths come from simple columnar or cuboidal, or stratified squamous epithelia. While specific reasons for this observation are not known, it clearly

• Relates to the very high rate of cell proliferation that is normal for epithelial tissues.
  • In the normal condition for the gastrointestinal tract, for example, the entire epithelial covering, from mouth to anus, is completely replaced every five days.
• To the right is an example of a benign colon polyp, representing the localized, excessive proliferation of the columnar epithelial lining. The picture was taken during colonoscopy.

You need to know the difference between cilia, and microvilli.