We thank our colleagues Barreto and Shukla for their interest in our work and for their comments. They are right, the concept of circulating tumor cells is not new. In fact, circulating cells in blood were first described not in 1955 by Engell, but—to our knowledge—in 1917 by Marcus.1
Barreto and Shukla remark that disseminated cells are epithelial cells and that the labeling we used was not tumor-specific. This is correct. However, we had no better choice than these antibodies when our study started in 1997. Moreover, in the meantime, the markers we used have been applied in a large number of prognostic studies on minimal residual disease in various cancers. It is indeed unfortunate that no specific tumor markers are available for immunohistochemical characterization of circulating epithelial cells. This was the reason why our group started early molecular studies on this topic; we were the first to investigate the clonality of disseminated tumor cells of colorectal origin in bone marrow on the basis of mutations in the K-ras codons 12 and 13.2
Steinert R, Reymond MA. Demonstration of the Presence of Circulating Tumor Cells as Evidence of Metastatic Potential—Reply. Arch Surg. 2008;143(11):1134. doi:10.1001/archsurg.143.11.1134-b
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