ALDH1A1 and colorectal carcinoma: Future immunohistochemistry co-localization studies in CRCs of DKK-1 and CCIC markers such as ALDH1 or CD44/CD166 (and in parallel co-localization studies with non-CCIC CRC cell markers such as CEA) will be useful to understand the precise role of DKK-1 expression in both CCIC and non-CCIC CRC cells.