  An unprecedented number of new cancer targets are in development, and most
are being developed in combination therapies. Early oncology development is
strategically challenged in choosing the best combinations to move forward to
late stage development. The most common early endpoints to be assessed in such
decision-making include objective response rate, duration of response and tumor
size change. In this paper, using independent-drug-action and
Bliss-drug-independence concepts as a foundation, we introduce simple models to
predict combination therapy efficacy for duration of response and tumor size
change. These models complement previous publications using the independent
action models (Palmer 2017, Schmidt 2020) to predict progression-free survival
and objective response rate and serve as new predictive models to understand
drug combinations for early endpoints. The models can be applied to predict the
combination treatment effect for early endpoints given monotherapy data, or to
estimate the possible effect of one monotherapy in the combination if data are
available from the combination therapy and the other monotherapy. Such
quantitative work facilitates efficient oncology drug development.
