Metastasis: Circulating Tumor Cells in Small Cell Lung Cancer.

Small cell lung cancer (SCLC) is distinguished by excessive numbers of circulating tumor cells (CTCs) in extended and recurring disease. This malignancy has a poor prognosis due to rapid emergence of chemoradioresistant relapses after first-line chemotherapy. In vitro expansion of several CTC lines allowed for a detailed study of the contribution of these cells to metastasis. Generation of CTCs involves the establishment of co-cultures and recruitment of macrophages and specific cytokines. All cell lines show E-cadherin-positive epithelial-like cells and spontaneous assembling into very large tumorospheres. Such multicellular aggregates seem to be responsible for the observed broad resistance due to limited access to drugs, quiescent cell layers, and hypoxic cores.