While the scope of these studies is complex given the multi-compartment distribution of CTCs/DTCs, in general they evaluate one or more of the following variables: (i) expression of ALDH in primary tumors in correlation with CTCs/DTCs, (ii) expression of ALDH in CTCs/DTCs as a stem cell marker and its correlation with clinical prognosis and metastatic activity; and/or (iii) co-expression of ALDH with other known markers of stem-like behavior and cancer progression in CTCs/DTCs. This evidence concerns the gene LDHA and cancer.