In a November 2 Federal Register notice (available at, the U.S. Food and Drug Administration (FDA) announced availability of a final guidance document, “S1B(R1) Addendum to S1B Testing for Carcinogenicity of Pharmaceuticals.” The guidance was prepared under the auspices of the International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use, and offers an integrative approach that provides specific weight-of-evidence criteria that inform whether a 2-year rat study is likely to add value in completing a human carcinogenicity risk assessment. This final guidance considered comments received from the public in response to release of the draft guidance in October 2021, and is available at