There are several treatment options to address breast cancer, depending on the severity of the cancer. But with some treatments, side-effects and reactions come that can affect some patients. Since not everyone is the same, patients may react in different ways to the same treatment. Some of the side-effects that may happen are allergic reactions. These may happen when your body is sensitive to a specific substance. To help you learn more about what types of allergic reactions can happen, we've put together a list of five mild reactions that can happen due to breast cancer treatment (source: BreastCancer.org): Symptoms of a rash may include redness, itching, inflammation, bumps, dryness, blisters, swelling and pain. Find out 6 signs and symptoms of breast cancer.