I have not heard of one that size, here is some information I found.
Occasionally, a polyp is too large to be removed endoscopically, usually when the diameter is more than about 4cm and, particularly, if the base of the polyp is broad with no well-defined stalk. In these cases, endoscopic removal can carry an unacceptably high risk of bleeding or perforation.
Types of polyp
Metaplastic polyps versus adenomatous polyps
The most common sort of polyp is a metaplastic polyp (in which cells change from one normal type to another). These usually do not grow much more than 5mm in diameter and have almost no risk of becoming malignant (cancerous). These polyps can be very similar in appearance to adenomatous polyps, the next most common type, which do have the potential to become malignant
Hope this helps..
Tammy Figg
www.figgtree.com