CCKBR and medullary thyroid gland carcinoma: CCK2R is not only expressed in ECL cells and promotes heterogeneous proliferation but is also highly expressed in a variety of tumour tissues, such as pancreatic cancer, colorectal cancer, medullary thyroid cancer, etc. At present, CCK2R has become a target for radiotherapy of tumours, and radiopharmaceuticals that can effectively bind to CCK2R are being studied to target tumours and improve the effectiveness of radiotherapy [22].