The present invention relates to a systems and methods for selecting agents and combinations of agents for treatment of particular cancer patients or selected groups of cancer patients. These methods of the invention index possible agents and combinations in a ranking indicating the likelihood of their usefulness in the particular patient or group of patients. The indexing depends on chemo-sensitivity/resistance assays data for the agents and combinations themselves, supplemented by reference data obtained from assaying the same and other agents and combinations against clinically similar tumors, and on overall clinical response rates for the agents and combinations. These methods include additional new indexing criteria which supplement or replace previous criteria in order to provide for more complex, informative and quantitative analysis of potential treatments for single patients or groups of patients. The new criteria, and the methods and the present invention generally, are based on new discoveries and insights concerning the action and interaction of chemotherapeutic agents, including for example, recognition of the common heterogeneity of tumors heretofore considered empirically substantially homogeneous. Systems of the invention provide access to significant reference data and implement the methods of the invention in a manner for use by physicians and other health professionals. In further embodiment, these method and systems provide for screening of new agents and new combinations including, perhaps, old agents in a manner that can detect activity even if overall clinical response rates are not encouraging.