NOTCH3 and neoplasm: In patient tissue, both NOTCH1 and NOTCH3 are overexpressed in tumour cells compared to adjacent non-cancerous bile ducts, and, by contrast, expression of NOTCH2, which is critical for ductular formation in the embryo, does not appear to appreciably change between pre-neoplastic and neoplastic states (Guest et al., 2016; O'Rourke et al., 2020).