After completing neoadjuvant chemotherapy for triple-negative invasive breast cancer, Madeline, age 32, had a bilateral mastectomy with reconstructive surgery. Final pathology showed residual disease in the breast and one lymph node, and her oncologist recommended adjuvant therapy with capecitabine (1,500 mg twice a day for 14 days, off for 7 days). Five weeks postoperatively, she started cycle 1. Eight days later, her husband called the cancer clinic reporting that over the past two days, his wife developed profound weakness, unremitting diarrhea despite using diphenoxylate and atropine as directed, and painful, red, swollen hands and feet. Her symptoms represented a drastic change from her usual routine and energy level.