Breast cancer occurs with the formation of malignant tumors in the breast tissue. Symptoms can include: lump in the breast, a change in breast shape and size, drainage from the nipples, dimpling of the skin, and red patches on the skin of the breast. Find out more about how breast cancer can be diagnosed. There are several treatment options available for breast cancer, but some side effects may occur. Fatigue is a common side effect. Here's a list of five possible causes of fatigue in breast cancer patients. (source: BreastCancer.org) 1. Surgery can disturb your normal body rhythm which can result in tiredness that lasts longer than it should. General anesthesia, discomfort after your breast cancer surgery, and restricted activity can also make you feel exhausted. Here are 7 breast cancer surgeries you should know about.