How Is a Cancer of Unknown Primary Staged?

Most types of cancer are given stages I, II, III or IV based on the size of the cancer, growth into nearby organs, and whether or not the cancer has spread to lymph nodes or distant organs in the body. Stage I is the least extensive, and the patients with this stage have the best outlook for a cure. Stage IV cancers have the most extensive spread and tend to have the poorest outlook.

For different types of cancer, each staging system is somewhat different. In order to know a cancer’s stage, you first have to know where it started. Since the type of cancer is not known, it’s not possible to accurately stage cancers of unknown primary (CUPs). Nonetheless, to be considered a CUP, the cancer must have spread beyond the primary site. So all CUPs are at least a stage II, and most of them are stage III or IV.

Even though a patient’s exact stage may not be known, it’s still possible to make some predictions about prognosis (outlook) based on which organs are affected by the cancer. For example, if the cancer is only found in lymph nodes in one area or in a single organ, the outlook tends to be better than if the cancer is found in many different organs. Of course, other factors, such as how the cancer cells look under a microscope, how well the cancer responds to treatment, and a person’s overall health also play a role.