title: Interpretation of changes in circulating tumor cell counts.
abstract: The presence of circulating tumor cells (CTCs) in the blood of cancer patients may guide the use of therapy. We investigated how to evaluate a reduction in the number of CTCs after administration of therapy. CTCs were enumerated with the CellSearch system in 111 metastatic breast and 185 metastatic prostate cancer patients before start of a new line of chemotherapy and after initiation of therapy. Different means to express changes in CTC counts were evaluated with respect to overall survival (OS). A static CTC cutoff is the best method to determine whether a therapy is effective. This is exemplified by the highest Cox hazard ratio of 2.1 for OS; three methods to express relative differences performed worse. A lookup table is provided from which the significance of a change in CTCs can be derived. The aim of therapy should be the elimination of all CTCs. A period of 10 to 12 weeks of therapy is needed to reach the treatment effect on CTCs.
authors: Department of Medical Cell BioPhysics, University of Twente, Enschede, Netherlands.
authors: Frank Aw
authors: FA
authors: Coumans
authors: Sjoerd T
authors: ST
authors: Ligthart
authors: Leon Wmm
authors: LW
authors: Terstappen