Breast cancer stem cells characterized by CD70 expression preferentially metastasize to the lungs

Cancer stem cells (CSCs) are believed to form metastases. We sought to determine whether CD70 + subpopulation in human breast cancers represents the CSCs accounting for distant metastasis.

We measured the expression levels of CD70 in breast cancer cell lines and 122 primary breast cancer samples. We characterized the functional roles of CD70 + subpopulation in distant metastasis of breast cancers.

We observed a distinct pattern of CD70 expression in a panel of primary breast carcinoma samples, indicating that CD70 serves as a biomarker of lung-specific metastasis. CD70- and CD70+ cell populations isolated from breast cancer cell lines exhibited epithelial and mesenchymal phenotypes, respectively. CD70+ cells, but not CD70- cells, possessed self-renewal and differentiation potentials. Tumorsphere formation in suspension cultures and in vivo tumorigenicity were significantly greater in CD70+ cells than in CD70- cells. Furthermore, the development of lung metastases induced by orthotopic injection was markedly increased in mice inoculated with CD70 + cells. CD70 contributed to the promotion of lung metastases by enhancing self-renewal potential of CD70 + cells.

We isolated CSCs from primary human breast cancers and found that CD70 + subpopulations mediate lung-specific metastasis. These findings might be used to aid in selection of patients for postoperative adjuvant therapy.