Cancer is the growth of abnormal cells in the body. Cancer can develop in any part of the body and form a mass of tissue called a tumor. At times, cancer can go undetectable, but a mass on the body is a distinct symptom that should be tested. There is no single cause of the uncontrolled growth of cells, but if caught early, it can be treated. There are several methods of cancer screening, depending on the site of your concern. Mammograms can be used to help detect breast cancer.