Effect of Spalax, rat and mouse fibroblasts on Spalax -derived fibrosarcoma cells colony formation. (A) SpFS2240 Cancer cells were grown in soft agar on top of monolayers of mouse, rat and Spalax fibroblasts. After three weeks, colonies were counted. At least 10 fields were recorded for each observation. Two representative images demonstrating effects of different fibroblasts on colony-formation are shown (×40). (B) Colony numbers and cumulative total colony area (μm2) from five fields were calculated to demonstrate the effects of the fibroblasts monolayer on the cancer cell colony formation and growth.