How much chemo can a body take

My wife was diagnosed with Stage 3C Ovarian cancer Sept 2003. Her CA125 was 4900. After debulking, she started her chemo treatments. She has had 7 treatments of Carbo and taxil, then had a reaction, switched to 26 treatments of Topo. At the start of the topo treatments, her CA125 dipped down to 78 but started to climb up. Chemo was changed to Doxil where she had 5 treatments and her CA125 increasing. She was changed to Gemzar where she has had 6 treatments so far. Her latest CA125 was 3970.

I may add that she feels fine (but tired) and is able to work every day. She has never had any illness or reactions to the chemo (except for the one while being infused with carbo). I realize that the cancer is growing, but how much chemo can a body take before it caused serious damage to the organs and should the doctor take another look inside. She did have a cat scan in March.