Introduction: From the early days of pathology back in the nineteenth century until now, there has been an ongoing search for the missing link between solid tumors such as breast cancer and distant metastases, which sometimes occur many years after removal of the primary tumor. The "seed and soil" theory hypothesizes the early dissemination of occult tumor cells into blood or bone marrow, which can persist in a dormant state for a long time and then become precursors of metastases in distant organs which offer appropriate conditions.
Method: Advances in immunocytochemical methods have enabled the enrichment and visualization of those disseminated tumor cells in bone marrow (DTC-BM) or circulating tumor cells (CTC) in blood. Many studies could demonstrate prognostic significance of the detection of DTC-BM or CTC in different stages of breast cancer.
Conclusion: Further characterization of those cells by immunocytochemical stainings, fluorescence in situ hybridizations, or PCR-based molecular methods will help to understand the biology of tumor cell dissemination and metastasis formation, as well as to define potential drug targets.
Keywords: Bone marrow; Breast cancer; Characterization; Circulating tumor cells; Detection; Disseminated tumor cells; Enrichment; Targets.