Keywords: efficacy evaluation metric, tumor response kinetics, immunotherapy studies
Immune checkpoint inhibitors have demonstrated unique tumor response and progression kinetics, such as durable response, pseudo-progression and/or delayed response. These features lead to questionable utility of conventional efficacy endpoints such as response rate and progression-free survival in early phase Go-No Go decisions. We propose a novel and clinically interpretable summary measure as an alternative early phase (phase I/II) efficacy evaluation metric. Unlike the conventional metrics which evaluate tumor responses within a specific landmark time (e.g., 12 weeks, 24 weeks, etc.), this novel metric integrates the longitudinal process of tumor response kinetics from randomization to a landmark time. Intuitively, this metric will be more informative as it incorporates temporal information and helps separate patients who have durable response and disease control from the rest, and thus has the immediate application to expedite early-phase oncology drug development. We illustrate this metric on historical data retrospectively from several completed immunotherapy studies and describe the features and limitations of the proposed metric.