The reviewer is correct that a native FHIR field (statusReason) is available and can be used to carry the treatment termination reason. It is preferable to use native fields over extensions when available. We propose to retire the TreatmentTerminationReason extension, and instruct the use of statusReason instead. A detail here is that the codes for termination reason only apply when `status = #stopped` so there will have to be new invariants that enforce the relationship beetween status and statusReason. For backward compatibility, we will leave the structure definition of the extension in mCODE in STU 3, to be removed at a later date.