Reports of a suspected cancer cluster can be frightening for any community. The source of a cancer cluster is often the primary community concern, but it is inherently difficult to link a cluster with any specific environmental agent. This thesis focuses on aspects of cancer clusters such as the official cancer cluster definition and investigation guidelines given by the Centers for Disease Control and Prevention. It explores “Cancer Clusters in the USA: What do the last twenty years of state and federal investigations tell us?” [1], an article which reviewed publicly available cancer cluster investigation reports from 1990 to 2012, and uses a similar methodology to review investigation reports from 2012 to 2016 in the interest of providing more modern data regarding cancer cluster reports.