In final guidance for biosimilar mAbs in May, EMA laid out a step-by-step checklist in which it said sponsors can use pharmacodynamic markers as "pivotal evidence" of comparable efficacy to the reference mAb. The guidance requires that PD markers show a clear dose-response relationship and that at least one marker be an accepted surrogate that correlates to patient outcomes. Draft guidance released in 2010 said clinical studies were needed when PD studies cannot "convincingly" show comparability in a "clinically relevant manner." The guidance requires sponsors to first conduct non-clinical pharmacokinetic/pharmacodynamic and toxicity studies before moving into clinical testing, if necessary. Clinical testing would include small PK studies, preferably in healthy volunteers, and then PD studies. If the PD studies do not show comparability