Grading and Staging of Cancer
What is grading of cancer?
Histologic "grade" is sometimes to used to describe what a cancer looks like microscopically. Most cancers are graded by how much they look like normal cells. Well-differentiated (low grade or grade I) tumors look more like normal tissue. Poorly differentiated (high grade or grade III) tumors look disorganized under the microscope and may behave more aggressively than grade I tumors. Those tumors that look neither well-differentiated nor poorly differentiated are designated moderately differentiated, or grade II. The histologic grade can suggest how slow growing (grade I) or aggressive (grade III) a tumor is.
What is staging of cancer?
Once cancer is diagnosed, more tests will be done to find out the size of the tumor and whether the cancer cells have spread to other parts of the body. This testing is called staging. To plan treatment, a healthcare provider needs to know the stage of the disease. Stage refers to the extent, or the size, of the cancer and whether it has spread from where it started. Each cancer, by organ, has its own staging system. In most cases, the stage is labeled with 0 and Roman numerals I through IV, with stage IV being the most advanced stage.
Stages of cancer (the following list is general; each tumor type has its own [and sometimes, complex] staging system)
Stage 0 or carcinoma in situ. Carcinoma in situ is very early cancer. The abnormal cells are found only in the first layer of cells of the primary site and do not invade the deeper tissues. This stage is referred to as pre-malignant or pre-cancerous.
Stage I. Cancer involves the primary site, and is considered early stage and most curable.
Stage II. Cancer involves the primary site. It may be a bit larger than stage I disease or involve nearby lymph nodes.
Stage III. Cancer involves the primary site and involves nearby lymph nodes.
Stage IV. Cancer has spread to other parts of the body (metastasized).
Recurrent. Recurrent disease means that the cancer has come back (recurred) after it has been treated. It may come back in the same area or in a different part of the body.
Higher numbers usually mean more extensive disease, larger tumor size, and/or spread of the cancer beyond the organ in which it first developed. Once a stage is assigned and treatment given, the stage is never changed. For example, if a stage I cancer of the cervix is treated, and 2 years later a metastasis (spread of the same cancer) is found in the lung, it is not now stage IV, but remains a stage I, with recurrence to the lung.
The important thing about staging is that it determines the appropriate treatment, helps healthcare providers make a prognosis, and allows for comparison of treatment results.