Staging for cancer of unknown primary

Most types of cancer are given a stage (I, II, III or IV) based on how much the cancer has spread from the place where it started. As a rule, stage I is the least widespread and has the best outlook. Stage IV is a more advanced cancer with a more serious outlook. For each type of cancer, the staging system might be somewhat different.

Cancer of unknown primary (CUP) can’t be staged this way because the exact type of cancer is not known. Since CUP has already spread beyond the place where it started, all cases of CUP are at least a stage II, and most of them are a stage III or IV.

Even though a person’s exact stage may not be known, doctors can still make some guesses about the outcome based on which organs are involved. For instance, 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.