When diagnosed with cancer, patients are typically informed where the cancer is or, when the cancer is in an advanced stage, where it started. However, in some instances doctors struggle to determine the origin of a cancer in the body.
According to the Canadian Cancer Society, cancer of unknown primary, commonly referred to as CUP, means that the cancer has already metastasized at diagnosis and doctors do not know where it started. Upon further testing, the primary site for the cancer might be identified, but in many cases doctors never learn where the cancer began. In some instances, the primary cancer can be identified thanks to the cancer cells' appearance. The cancer cells usually look like the cells in the type of tissue in which they began. For instance, if breast cancer cells spread to the lungs, the cancer cells in the lung will look like breast cancer cells, giving doctors a good idea of where the cancer might have begun. But the primary cancer may not be found for a number of reasons, including:
*The primary cancer is very small and grows slowly,
*The primary cancer was actually killed by the body's immune system,
*The primary cancer was removed during surgery for a different condition and doctors never realized a cancer had formed.
A CUP diagnosis is not especially common, though the CCS estimates that roughly two to five percent of all new cases of cancer are CUP. The figures are similar in the United States, where the American Cancer Society estimates that two percent of all cancers, or roughly 30,000 diagnoses, are CUP.
Because they depend on where the cancer has spread in the body, CUP's signs and symptoms are different depending on each individual case. However, symptoms can include: a lump or thickening in any part of the body, a persistent pain in one part of the body, a change in bowel or bladder habits, including constipation, diarrhea or frequent urination or a persistent fever for no known reason that does not go away.
Other symptoms include unusual bleeding or discharge, night sweats or a persistent cough or hoarseness in the voice.
Despite unawareness as to its origins, CUP can be treated. In such cases, doctors will look at the cancer cells under a microscope, study lab results and then consider which organs the cancer has affected before determining a course of treatment. Determining the treatment strategy, however, is not easy, as doctors do not often find the origin of the cancer. In addition, CUP often involves fast-spreading cancers, most of which are already widespread upon diagnosis. The ACS reports that the average survival time is 9 to 12 months after the cancer is found.
More information on CUP is available at www.cancer.org and www.cancer.ca.