Brief Summary: Colon polyposis (the presence of multiple colon polyps) is very common with Cowden syndrome, as over 60% of patients have 50 or more polyps. In a previous clinical trial, some participants had reduction in the number of colon polyps with the use of the medication sirolimus for a very short time period. This study is investigating sirolimus and its effect on the number of colon polyps in patients with Cowden syndrome and polyposis over a 1 year period.

Detailed Description: PTEN is a tumor suppressor gene that regulates the cell cycle through the phosphoinositide 3-kinase (PI3K)/Akt/mTOR pathway. When germline mutations in PTEN occur, the result is Cowden syndrome (or less commonly one of several related disorders collectively called the PTEN hamartoma tumor syndrome). This is characterized by the growth of hamartomas and a high risk of cancer in multiple organ systems. This includes colon polyps in 92.5% of Cowden syndrome patients and 64% with an estimated 50 or more polyps. Although outcomes of this are under reported, series suggest 20-38% of patients will receive colectomy. Current clinical practice for Cowden syndrome is based on close surveillance for the development of cancers. Sirolimus (also known as rapamycin) is a specific inhibitor of mTOR that is FDA-approved for immunosuppression and use in several types of cancers as chemotherapy. It has also been used successfully in other hamartomatous syndromes including lymphangioleiomyomatosis. There is also a completed pilot clinical trial for adults with Cowden syndrome in which some had reduction in the number of colon polyps with the use of the medication sirolimus for a very short time period. This will be an open-label pilot trial to determine whether sirolimus reduces colon polyp burden in Cowden syndrome. Sirolimus will be administered for one year. Colonoscopy with polyp estimation will be performed at trial entrance and at study completion.