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​Medically reviewed by C.H. Weaver M.D. Medical Editor updated 12/2020

The treatment of a cancer may include the use of chemotherapy, radiation therapy, targeted therapy, surgery, or some combination of all of these or other therapeutic options. All of these treatment options are directed at killing or eradicating cancer cells. Unfortunately, cancer treatments may also damage normal, healthy cells that are not affected by the cancer. The result of this damage is a complication, or side effect, of treatment.

Why do side effects occur?

Side effects occur because most cancer treatments cannot distinguish between cancer cells and normal, healthy cells. For example, chemotherapy damages rapidly dividing cells, a hallmark trait of cancer cells. In the process, healthy cells that are also rapidly dividing, such as blood cells and the cells lining the mouth and GI tract are also damaged. Radiation therapy kills some healthy cells that are in the path of the radiation or near the cancer being treated. Newer radiation therapy techniques can reduce, but not eliminate this damage.

Why are side effects important?

Side effects of treatment cause inconvenience, discomfort, and occasionally even fatality to patients. Additionally, and perhaps more importantly, side effects may also prevent doctors from delivering the prescribed dose of therapy at the specific time and schedule of the treatment plan. This is extremely important to understand since the expected outcome from therapy is based on delivering treatment at the dose and schedule of the treatment plan. In other words, side effects not only cause discomfort and unpleasantness, but may also limit a patient’s ability to achieve the best outcome from treatment by preventing the delivery of therapy at its optimal dose and time.Fortunately, in the last 15 years there has been a great deal of progress in the development of treatments to help prevent and control the side effects of cancer treatment. These compounds have led to vast improvements in the management of symptoms associated with cancer treatment, allowed for greater accuracy and consistency concerning the administration of cancer treatment, and have made many cancer treatments more widely available to patients throughout the world.

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Common side effects

Side Effects of Immunotherapy

Less Common Side Effects of Cancer and its Treatment

  • Blood flow Problems Bruising and Bleeding Blood Clots Superior Vena Cava Syndrome Blood Test Abnormalities Electrolyte Imbalance Hypercalcemia Tumor Lysis Syndrome Common Cold Cough Flu-like Syndromes
  • Gastrointestinal Complications Abdominal Pains Constipation Diarrhea Heartburn
  • Swelling Lymphedema Water Retention
  • Sexual issues Impotence Vaginal Dryness
  • Mental/Emotional Problems Anxiety Forgetfulness Post-traumatic Stress
  • Nervous System Problems Confusion/Delirium Dizziness Numbness and Tingling Seizures
  • Nutritional Issues Dry Mouth Poor Appetite Taste Changes Cachexia
  • Weight Changes Weight Gain Weight Loss
  • Organ Problems Allergic Reaction Bladder Bone Pain Eyes Ears/Hearing Heart Kidney Liver Lung
  • Skin Reactions Dry Skin Flushing Hand-foot Syndrome Hyperpigmentation Injection Site Reaction Itching Photosensitivity Radiation Recall Rash

Long term side effects

Things you may need to know include the following topics