[Minimal residual disease in solid cancer. Prognostic value and therapeutic consequences]

Minimal residual disease (MRD) is one of the issues in solid carcinomas which is still discussed controversially as to its prognostic value and therapeutic implications. In the past, the evidence for MRD was especially given by immunocytochemistry for epithelial cytokeratin markers which were able to detect single disseminated tumor cells within the mesenchymal background of the bone marrow at sufficient sensitivity and specificity. However, for the perioperative detection of disseminated tumor cells, numerous studies have given controversial results regarding the prognostic relevance of these cells. Some other studies investigating the postoperative development of disseminated tumor cells in the bone marrow after curative tumor resection observed substantial changes in status over time, suggesting that microenvironment interactions and phenotypic characteristics of these cells rather than the mere evidence of MRD will be able to indicate the stage of systemic disease which is of metastatic and prognostic relevance. Currently, new molecular biology techniques are applied to achieve the objective of MRD phenotyping which has good chances of providing new models for a new molecular tumor staging. Based on this development, targeting biologically relevant disseminated tumor cells will most likely become an important issue in carcinoma therapy, and first therapeutic studies are under way. However, at the present time, the mere screening for disseminated tumor cells must still be seen as a very helpful diagnostic tool for monitoring MRD especially in the setting of follow-up, rather than being able to be a key essential in therapeutic applications.