The present disclosure generally relates to systems and methods for partitioning species. In some embodiments, such systems can be used for determining one or more types of cancer. For example, certain aspects are generally directed to aqueous multi-phase partitioning systems that can be used, for example, for distinguishing between different types of cancers, diagnosing subjects with cancer, or the like. In some cases, such systems can be identified using solvent properties such as the solvent dipolarity/polarizability difference (Δπ*), the solvent hydrogen bond donor acidity difference (Δα), the solvent hydrogen bond acceptor basicity difference (Δβ), and the electrostatic property difference (c) between two phases of the partitioning system. These may be within certain ranges in accordance with various embodiments. Additionally, these ranges can be precisely tuned by controlling the compositions of the phases of the partitioning system to produce novel partitioning systems that are unexpectedly efficient at distinguishing between even relatively minor structural changes of proteins or other species, which accordingly can be used to distinguishing different types of cancers, or for other applications.