FDA draft guidance on “Co development of two or more unmarketed investigational drugs for use in combination”  notes that:

“Combination therapy is an important treatment modality in many disease settings, including cancer, cardio-vascular disease, and infectious diseases. Recent scientific advances have increased our understanding of the pathophysiological processes that underlie these and other complex diseases. This increased understanding has provided further impetus for new therapeutic approaches using combinations of drugs directed at multiple therapeutic targets to improve treatment response or minimize development of resistance.” In this setting, it’s important to be able to design dose escalation studies which can identify the synergistic activity of compounds, and less toxic combinations.