Retrieval of Disseminated Tumor Cells Colonizing the Bone in Murine Breast Cancer Metastasis Models

Thomas Welte, Cuijuan Yu, Xiang H.-F. Zhang

In breast cancer, the most frequent site of metastasis is bone. Disseminated tumor cells (DTCs) can be detected in the bone marrow of patients by their expression of epithelial or oncogenic markers [1], and the presence and frequency of these DTCs are associated with poor prognosis. However, many of the details behind this process remain elusive, including the biological properties and fates of these apparently indolent cancer cells. To provide pre-clinical models of DTCs, we have developed a procedure that allows for controlled and enhanced delivery of tumor cells to the bone in animal experiments via injection into the iliac artery of the hind limb [2]. To our surprise, we found that most cancer cells became integrated into the solid bone matrix shortly after arriving in the bone, and only a minority can be flushed out with the bone marrow. Here we describe a method that helps to retrieve DTCs homing to the bone in which we achieve an improved recovery of those tumor cells closely associated with the bone microenvironment. In our view it is especially important to analyze these tumor cell subpopulations, as they may take full advantage of growth-, survival- and immune-protective signals provided by neighbor cells. We also show a pilot study on how this approach may be applied to the analysis of cancer dormancy. Our study suggests that the detection and retrieval of DTCs in clinical studies are incomplete because they are conducted exclusively with bone marrow aspirates.