DKK1 and breast cancer: More importantly, elevation of both serum DKK1 levels detected by enzyme-linked immunosorbent assay (ELISA) and DKK1 protein levels assessed by immunohistochemistry has been found in different kinds of cancers including breast cancer, pancreatic ductal adenocarcinoma, esophageal squamous cell carcinoma, and non–small cell lung cancer, and this was in accordance with the cancer metastases or poor prognosis (31–33).