Circulating tumor cells in breast cancer: correlation to bone marrow micrometastases, heterogeneous response to systemic therapy and low proliferative activity. - Müller,V.; Stahmann,N.; Riethdorf,S.; Rau,T.; Zabel,T.; Goetz,A.; Jänicke,F.; Pantel,K. (Clin Cancer Res, 2005)