Circulating Tumor Cells in Metastatic Breast Cancer — Toward Individualized Treatment?

When Steven Paget published his theory of “seed and soil” in 1889,1 the idea of hematogenous tumor-cell dissemination was born. More than a century later, with the use of molecular tools, new clinical findings have resulted in explanations of hither-to unexplainable phenomena, such as that donor-derived cancer in recipient organ allografts2 and viable single tumor cells in secondary organs were both the descendants of a known primary tumor3 and the potential precursors of subsequent metastasis.4 Now, as shown by Cristofanilli et al.5 in this issue of the Journal, a laboratory assay of circulating tumor cells enables us to predict a . . .