On November 9, BIO submitted comments on the FDA Draft Guidance, Drug-Drug Interaction Assessment for Therapeutic Proteins. In the comments, BIO thanks the FDA for the opportunity to submit comments but requests that the Guidance include a discussion on the potential of generalizing information between ADCs that share the same payload and for further information to understand, from FDA’s perspective, under what conditions it would be possible to apply information from a DDI study conducted using an ADC to another ADC that had the same payload. Additionally, while the Guidance focuses on CYP-related DDIs, BIO suggests clarifying when there should be assessments for potential transporter related DDIs with TPs [1],[2]. If FDA decides to include such a discussion, potentially as part of Section III.B (pages 5-6; starting at line 196), endogenous CYP/drug transporter substrates may help define the potential for clinically significant DDIs. BIO appreciates the opportunity for sponsors to consider the specifics of their particular therapeutic proteins in the context of specific indications and concomitant medications and propose a fit-for-purpose development strategy in consultation with the Agency. In addition, the recognition of the potential contribution and value of model-based analyses, such as PBPK modeling, affords additional tools to interrogate the potential for DDIs and make informed decisions or scientific justifications. BIO looks forward to final guidance on this topic.