CPCs have been shown to express membrane MMP-2; tumor cells detected in bone marrow aspirates may also express MMP-2; however, on implanting in bone marrow the micrometastasis from low grade tumors and surrounding stromal cells are negative for MMP-2 expression, while in higher-grade cancers the micrometastasis retain MMP-2 expression [106, 107]. This evidence concerns the gene MMP2 and cancer.