Since the ICH guidance S9 Nonclinical Evaluation for Anticancer Pharmaceuticals was finalized (ICH S9 or ICH S9 guidance), all parties using the guidance have experienced some challenges with implementation of the recommendations on nonclinical evaluation for anticancer pharmaceuticals. This question-and-answer guidance is intended to facilitate the implementation of ICH S9, as well as to continue progress in the 3Rs of Reduction, Refinement, and Replacement in the use of animals.