Methods and kits for detecting the activation states of a plurality of signal transducers of circulating cells of a solid tumor in a specific, multiplex, high-throughput assay are described. The methods comprise: contacting the signal transducers extracted from the cells with first, second, and third binding partners specific for each of the signal transducers to produce signal transducer-binding partner complexes. The second binding partners bind the corresponding signal transducers independent of their activation state and are labeled with a first moiety, and the third binding partners bind the corresponding signal transducers dependent of their activation state and are labeled with a second moiety. The first and second moieties are detected as an indication of the activation states of the plurality of signal transducers.