The expression level of the HER family is unreliable as a predictive marker for 
targeted therapies in cancer. Thus, there is a need to develop other biomarkers, 
which can be used to accurately select responsive patients for targeted 
therapies. The HER dimerization status may be more important than HER receptor 
expression per se in determining sensitivity or resistance to a given 
therapeutic agent. The aim of the study is to develop a FRET assay using dye 
conjugated secondary antibodies to assess HER receptor dimerization. Using 
primary antibodies from different species in conjunction with Alexa488 and 
Alexa546 conjugated secondary antibodies, we validated our EGFR/HER2 
dimerization assay in three cell lines, EGFR positive A431 cells as well as HER2 
positive breast cell lines BT474 and SKBR3 cells. Finally, we applied our assay 
to assess EGFR/HER2 dimerization in paraffin embedded cell pellets. Our results 
show promise for the assay to be applied to tumor samples in order to assess the 
prognostic significance and predictive value of HER receptor dimerization in 
various cancers.