I am working with thyroid cancer cell lines and I isolated like-cancer stem cells from them, I used the sphere formation assay and my cells grown in suspension like spheres and I was able to pass the spheres for several generations, to support the self-renewal. You can look this paper published by Setoguchi T et al, 2004 Cell cicle and Gene expression profiling of cancer stem cells in the Du145 prostate cancer cell line by Chen W, Wang GM. 2012 Oncology letters.