Hi. Some chemotherapy drugs commonly used for breast cancer, like fluorouracil, doxorubicin, docetaxel and paclitaxel cause diarrhea in a significant number of patients who receive these drugs. Your wife should take lots of fluids to avoid dehydration. She may also ask her oncologist for loperamide capsules to stop the diarrhea episodes. Alternatively the diarrhea may be infectious in origin (not a side effect of the chemo drugs), particularly if there is associated fever. If this is the case, your wife should consult with her oncologist because she may need to be given antibiotics for it.