As if dealing with a breast cancer diagnosis isn’t complicated enough, there are potential side effects like lymphedema that can occur during treatment and even years after treatment is completed. Lymphedema, when it occurs, is a build-up of lymph fluid usually in the arm, hand, breast or torso after lymph node removal or radiation therapy to a lymph node region. In most cases it develops slowly over time. Some breast cancer patients are never bothered by it. There’s no way to predict who will develop lymphedema.