General characteristics of tumor spheres formed from multiple cell lines.

<p><b>A</b>. Significant heterogeneity existed in the size of TS as shown by representative pictures of TS from H1299 and MCF7 cultured in TS medium for 8 days. Counting of smaller TS (solid arrow) was sometimes prone to subjectiveness. TS derived from certain cell lines (HCT116) might have strong tendency to fuse (hollow arrow). <b>B.</b> “size of spheres” for H1299 TS showed a skewed distribution with smaller spheres account for the majority of population. H1299 cells were plated in 24-well ULA plate (2000 per well in 2ml of TS medium) to allow TS formation for 4 days before microscopic assessment. The results were presented as Mean ± SEM from 6 replicates. <b>C</b>. Some tumor cell lines formed typical 3-dimensional spherical structures with sharp edges (A), while others were not, or require special supplement (hollow arrow).