The use of proximity ligation assays (PLA) has circumvented this in some ways with notable recent observations of endogenous heterocomplexes of 5-HT1A/FGFR-1 in rat hippocampal pyramidal neurons [40] and rat hippocampal astrocytes [45], muscarinic acetylcholine receptor 1 (M1)/FGFR1 complexes in hippocampal neurons [46], constitutive thyroid stimulating hormone receptor (TSHR) and IGF-1R in Graves orbital fibroblasts [47] and CB2R/HER2 complexes in HER2+ breast cancer patient biopsies [11]. Here, ERBB2 is linked to breast cancer.