The concept of cancer stem cells (CSCs) provides a new paradigm for understanding cancer biology. Here we report how culture conditions affect the characteristics of primary ovarian cancer cells. Cancer cells disaggregated from ovarian serous adenocarcinoma and maintained in serum-free system culture formed sphere cells that exhibited several properties expected for CSCs. These include self-renewal, overexpression of stemness genes as detected by QPCR analysis, greater tumorigenicity and enhanced drug resistance. The serum-free culture system enriched the percentage of CD133+/CD117+ expressing cells in sphere cells as determined by flow cytometric analysis, immunostaining and Western blot analysis. A cDNA microarray showed that there were 2111 genes exhibiting more than a 2-fold difference in expression. Subsequent ontological analysis revealed that a large proportion of the classified genes were related to cell communication, cell-cell adhesion, cellular development and extracellular matrix. We suggest that the sphere cell subpopulation may be a more reliable model than differentiated cells grown in the presence of serum for understanding the biology of primary ovarian cancer.

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