Histologic "grade" is used to describe what the cancer cells look like using a microscope. Most cancers are graded by how much they look like normal cells.  Low grade or grade I tumors are well-differentiated. This means that the tumor cells are organized and look more like normal tissue. High grade or grade III tumor cells are  poorly differentiated. This means that the tumor cells don't look like normal cells. They're disorganized under the microscope and tend to grow and spread faster than grade I tumors. Cancer cells that do not look well-differentiated or poorly differentiated are called moderately differentiated, or grade II. In general, cancer cells are graded using this scale. (Be aware that some may use grade 3 as the highest grade):

• Grade X: grade isn't known

• Grade 1: Well differentiated, low grade

• Grade 2: Moderately differentiated, intermediate grade

• Grade 3: Poorly differentiated, high grade

• Grade 4: Undifferentiated, high grade

Once cancer is diagnosed, your healthcare provider will do more exams and tests to find out the size of the cancer and where it is. These exams and test will also help tell whether the cancer has grown into nearby areas and if it has spread to other parts of the body. This is called staging. The stage of a cancer is one of the most important things to know when deciding on how to treat the cancer. 

Each cancer, by organ, has its own staging system. In most cases, the stages are listed as Roman numerals and can have a value of I through IV (1 to 4). The higher the number, the more advanced the cancer is. Letters and numbers can be used after the Roman numeral to give more details.

• Stage 0 or carcinoma in situ. Carcinoma in situ is considered pre-malignant or pre-cancer. Abnormal cells are found only in the first layer of cells in the place where the changes first started. The cells do not invade the deepr tissues. These cells may become cancer over time, so it's good to find and treat them before that happens. Most kinds of cancer do not use this stage. 

• Stage I. Cancer is only in the cells where it first started and the area is small. This is considered early stage and most curable.

• Stage II. Cancer is in the organ where it first started. It may be a bit larger than stage I and/or may have spread to nearby lymph nodes.

• Stage III. Cancer in the organ where it first started. It may be larger than stage II and may have spread to nearby lymph nodes and/or other nearby tissues, organs, or structures. 

• Stage IV. Cancer has spread to organs in other parts of the body ( metastasized). There may be cancer indifferent organs, but it's still the same type of cancer as where it first started. For instance, colon cancer that spreads to the liver is not liver cancer, it's stage IV colon cancer with liver metastasis. The cancer cells in the liver look like the cancer cells in the colon and are treated like colon cancer. 

• Recurrent. Recurrent 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 where it first developed. Higher grade and stage cancers tend to be harder to cure and often require more intense treatments. 

Once a stage is assigned and treatment given, the stage is never changed. For example a stage I cancer of the cervix is treated. Two years later, the same cancer has spread and is now found in the  lung.  It is not now stage IV, but remains 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.

Cancer grade and stage can be very complex and confusing. Be sure to ask your healthcare provider to explain these details about your cancer to you in a way you can understand.