An addendum is additional information added to your pathology report after it was finalized by your pathologist. Most addendums are added to the bottom of the original report. The purpose of an addendum is to communicate additional information which supports the original diagnosis or interpretation. For example, tests results such as immunohistochemistry, fluorescence in situ hybridization (FISH), next-generation sequencing (NGS) are often included in an addendum. The results of an internal or external consultation or review of your case may also be included in an addendum. Information that leads to a change in diagnosis should be reported as an amendment, not an addendum.