Cancer is the second leading cause of death in the United States. With an aging population of baby boomers there is an increase incidence of cancer diagnosed. Oncology emergencies occur as a result of the cancer itself or is consequential to the treatment. These life-threatening events are classified as structural or metabolic in nature and require immediate medical intervention and supportive nursing care. Understanding the risk factors, physiologic manifestations, preventative measures and medical treatment will guide critical thinking in applying the nursing process.