OPN3 and breast cancer: A number of GPCRs have been previously reported to be overexpressed in breast cancer, including CCR1, Opsin-3, CXCR4, PAR1, PAR2, EP2, EP4, GPR30 and the C3A anaphylatoxin chemotactic receptor [42,45], although whether any of these are regulated by RGS2 remains unknown.