Operable early stage breast cancer patients staged according to NCCN guidelines are subjected to bone marrow aspiration/trephine biopsy at the time of the definitive operation under general anesthesia. The specimen will be fixated in neutral tamponaded formalin and the sections will be examined by H&E and cytokeratin immunohistochemically. If disseminated tumor cells are identified ER (estrogen receptor), PR (progesterone receptor), HER2/neu will be studied. Disseminated tumor cells will be recorded quantitively and semiquantitatively. Results of the pilot study will be evaluated as observational study.