Target Sufficiency® enables direct, quantitative analysis of drug target systems in cells, tissues, and tissue models, including formalin-fixed, paraffin-embedded (FFPE) tissues. Drug targets can be measured in their diverse forms (including sequence or splice variants and post-translationally modified forms) together with their key protein co-regulators that constitute therapeutic target systems. Target Sufficiency® defines the target system in its native cell or tissue environment and enables development of more effective therapeutic strategies and personalized therapies.