It is not always important to know the exact extent of the cancer. The importance depends on what treatment is being considered. For example, say a woman and her doctor were considering an extensive operation to remove the entire womb and both ovaries for cancer of the cervix. It would be important to be as sure as possible that there were no traces of cancer in other parts of the body before doing such an operation. A number of tests would be advisable to check thoroughly for possible secondary deposits.
What if this woman was found to have secondary cancer deposits in her bones? After finding out about the possible alternatives, she could decide to have no actual anti-cancer treatment and to concentrate simply on relief of symptoms. In this case, whether or not she also had cancer deposits in the lungs or liver would make no difference to her treatment, unless she had symptoms which could be originating in these organs. It would also be unnecessary to know exactly which bones were affected, as long as they were not causing pain. Tests to determine the exact extent of her cancer would be unnecessary.
On the othe’r hand, she might decide to have chemotherapy treatment. In this case, tests to find out how well her liver was functioning might be necessary in order to work out the right dose of chemotherapy drugs. It wouldn’t be necessary to know just how many secondary deposits there were or which particular bones or other organs they were in, because the chemotherapy drugs would travel right through the body anyway.
There are three separate aspects to think about when assessing the extent of cancer—we need to know the extent of the primary growth, of lymphatic spread, and of blood-borne spread.