Establishment of tumor spheroids. (A) Schematic representation of the microarchitecture of tumor spheroids, avascular tumor microregions and developing micrometastases (based on Friedrich et al. ) highlighting the pathophysiological similarities and differences. On the right, representative tumor spheroids derived from 2×103 cells are shown in a 96-well plate and by transmission microscopy at 50× magnification. (B) Growth kinetics of cervical carcinoma tumor spheroids. 5×103 CaSki or SiHa cells were seeded, and tumor spheroid growth was monitored by phase contrast microscopy at 50× magnification. The solid spheroidal state (day 0 = d0) was used in all further experiments as starting point. Tumor spheroid growth is plotted as the volume of individual spheroids from six independent experiments (n = 6). Data are shown as mean ± SEM. Spheroid volume (in mm3) was calculated based on phase contrast image analysis by area determination using Fiji software . The size bar corresponds to 100 μm. A p value < 0.05 is marked as statistically significant (*).