This study gathers health information for the Project: Every Child for younger patients with cancer. Gathering health information over time from younger patients with cancer may help doctors find better methods of treatment and on-going care.

This randomized phase III trial studies metformin hydrochloride to see how well it works compared to placebo in preventing breast cancer in patients with atypical hyperplasia or in situ breast cancer. Chemoprevention is the use of certain drugs to keep cancer from f...