Hi Rancher,
Chemo works on the various stages of the cell cycle,
http://en.wikipedia.org/wiki/Cell_cycle and the reason there are several different chemotherapy medications in a "regimen" is to target the cells at the various stages of growth. This is to reduce the maximum number of cancer cells per treatment. Some cells will be in a growth stage, some in mitosis, and some resting. This is why more than one dose of chemo is necessary, to be able to catch the cells coming out of their "resting" phase.
Often cyclophosphamide and doxorubicin are given. Doxorubicin has the heart side effects (cardiomyopathy). These heart effects are DOSE DEPENDENT. A person can only have so much of it and then it is not allowed to be given again. As long as it is given in the appropriate dose these side effects shouldn't be a concern.
They will monitor her heart and the doxorubicin dosage will be checked, double checked, and triple checked. Dosages of chemotherapy are most often based upon body surface area calculations. BSA will be calculated before each treatment. It is really a one day at a time therapy and when it's over it will be a big relief.
Radiation simply targets a specific target area.
http://www.cancer.gov/cancertopics/factsheet/Therapy/radiation Often it will shrink a tumor although it doesn't always completely eradicate the primary tumor. If the primary tumor is identified and is shrunk enough by radiation, surgery may be a viable option. If surgery is not a good option, chemotherapy may be added.
Side effects happen in body locations of high cell turnover, like the intestinal tract (like the mouth area), and hair. This is because the medications are working to fight as many cells as possible, all at once in all different cell cycle stages. It's also why the side effects are so horrible. The cancer cells are highly prolific and the chemo will work faster on prolific cancer cells than on the non-cancer cells.
To find out more about your DW's specific regimen, you may ask her oncologist what medications are being used for her specific regimen. He or she will provide you with a list of medications that are given. There may be more than the two that I mentioned.
You may contact me at any time with any questions. I would be happy to answer them or find an answer for you. We will continue to keep your DW in my prayers for fast healing, strength, and blessings for a healthy body. She's very fortunate to have you by her side.