Bone marrow "micrometastases" of epithelial tumors: detection and clinicalrelevance

The detection and elimination of "micrometastases" or, more precisely, isol ated disseminated tumor cells or minimal residual disease is one of the mai n current topics in clinical oncology. Immunocytochemical and molecular, po lymerase chain reaction (PCR) based methods are the preferred methods. Bone marrow as a mesenchymal organ and a frequent location for distant metastas es is very suitable to study isolated disseminated tumor cells. Under optim al conditions one tumor cell among one million mononuclear bone marrow cell s can be detected by immunocytochemistry or molecular methods. The specific ity, however, varies significantly depending on the assay conditions used b y each individual group, with false positive rates below 1% and over 80% re ported. Immunocytochemistry with antibodies against different epithelial ma rkers has shown that the presence of isolated disseminated tumor cells in b one marrow is an independent prognostic variable in breast, colorectal, gas tric, and non-small cell lung cancer. Due to the lack of a standardized ass ay, however, comparison of the results between different groups is very dif ficult. Before the assessment for isolated disseminated tumor cells in bone marrow or other organs can be transferred into routine clinical practice, standardized methods: have to be developed which must be tested in multicen ter prospective trials.