The ICH S1B(R1) guideline, published on the ICH official website on August 4, 2022, gives an opportunity for the exemption of long-term rat carcinogenicity studies based on the results of the Weight of Evidence (WoE) evaluation. PMDA issued related guidelines on March 10, 2023, incorporating revisions to ICH S1B(R1) and establishing a consultation framework to discuss potential exemptions based on these guidelines. Critical points of implementation in Japan are as follows:

• A new category of PMDA consultation, “S1B(R1) consultation,” is now available to discuss the possibility of exempting a rat carcinogenicity study based on WoE.
• Pre-consultation meetings are mandatory for applicants wishing to implement this consultation.
• Documents submitted for consultation should include detailed background information, non-clinical and clinical result summaries, WoE approach summaries, and relevant attachments like references and investigator brochures.