ERBB3 and breast cancer: Proximity ligation assays (PLAs) frequently used to detect HER2-HER2 and HER2-HER3 dimers in breast cancers require probes targeting the intracellular domain (not ECD) of these receptors (Banappagari et al., 2013; Barros et al., 2014; Green et al., 2014; Kanthala et al., 2014; Spears et al., 2012).