Identifying Duplicate Cancer Cases Across State Boundaries: Pseudonymization as a Method to Encrypt Identifiers.

Identifying potential duplicate cancer cases across state boundaries has been a topic of interest for many years. Duplicate cases could distort our understanding of the burden of cancer in a state, region, or even nationally, and waste cancer surveillance resources. This paper reports a pilot quality improvement project to use a publicly available tool to encrypt a standard set of patient identifiers and then link cases across state boundaries as a way to identify and reconcile possible duplicate cases among a group of neighboring states. The paper describes the protocol, challenges, and preliminary results, and suggests future efforts.