Parallelism: considerations for the development, validation and implementation of PK and biomarker ligand-binding assays.

The goal of this article is to discuss the fundamental key questions around parallelism assessments: why to do it, when to do it and how to do it, with consideration for different molecule types and the scientific rationale that drives different approaches. Current practices for both PK and biomarker assays regarding which samples to pick, whether to pool or not pool samples, as well as generally accepted acceptance criteria are discussed, while also highlighting the many outstanding questions that remain. In order to reach the long-term goal of understanding and developing best practices for implementation of parallelism testing for both PK and biomarker assays, industry and regulators will need to keep the conversations going, and commit to generating and reviewing data for the purposes of our own education. Means to easily share data in open forums to facilitate and build common understandings should continue and will be necessary to expedite resolution of many of these questions.