What is a Stage and why is it important?
Cancer Staging provides a standardized way to classify the extent of disease.
For many types of cancer, the stage determines what treatment options are appropriate for the patient.
The most commonly accepted staging system, established by the American Joint Committee on Cancer (AJCC) and accepted by the International Union Against Cancer (UICC), is called the TNM system. Read more about the TNM system below.
It’s also important to realize that the Staging of Cancer is very much an evolutionary process.
If you took a Staging Manual from 1997 and compared it today’s edition, you would notice some changes.
As we learn more about cancer and advance further in its treatment, we modify its classification to better reflect how today’s understanding and therapies affect its prognosis.
The TNM staging system — What makes up a stage?
The three components that make up the TNM staging system are:
- Tumor
- Nodes (as in, lymph nodes)
- Metastasis
Tumor – this refers to the size and/or extent of the primary tumor itself. In general, the larger the number assigned to the T-stage, the larger or more advanced the primary tumor is.
T-stages sometimes are further subclassified. For instance, any breast primary tumor that is 2 cm or less is a T1. And breast tumors that are larger than 1 cm but still 2 cm or less are T1c.
Sometimes, a primary tumor cannot be found or cannot be evaluated (e.g., when there is a cancerous lymph node of “unknown primary”). In these cases, seeing a T-stage of TX or T0 is not unusual. Also, the designation of Tis indicates the presence of “in-situ” carcinoma, which is very early stage cancer that has not yet invaded into surrounding tissues.
Nodes – Cancer cells can travel from the primary tumor site into our lymph nodes. The lymph nodes are part of our normal lymphatic pathways– a network of ducts and nodes which carry normal body fluid called lymph. When cancer cells are found in lymph nodes, it is a sign of a more advanced stage of cancer, and treatment decisions are influenced.
An N-stage higher than N0 indicates that lymph nodes are involved. If the lymph nodes have not been assessed, a stage of NX is assigned.
Metastasis – When cancer travels away from the primary site and involves another organ, then we say that it has metastasized. To indicate this, we signify it with a stage of “M1″.
The overall stage
So a TNM stage is composed of a T-stage, N-stage, and M-stage. For instance, a breast cancer which has a 0.9 cm primary tumor, has no lymph nodes invovled, and is not metastatic, is classified as T1bN0M0.
Similarly treated TNM cancers with similar outcomes are grouped together and given an overall stage.
In the case of breast cancer, T0N1M0, T1N1M0, and T2N0M0 are all grouped under Stage IIA.
Clinical and Pathologic Staging
It’s also important to differentiate what information was used to come up with the stage.
If the stage was established based upon imaging studies or doctor’s physical exams, then this is called a Clinical Stage.
After a surgical procedure, such as a lumpectomy with an axillary lymph node dissection, we can have an even more accurate measurement of the primary tumor or number of lymph nodes involved, after the pathologist looks at the specimen under the microscope, and carefully measures the tumor size of sees if there are any cancer cells present in the lymph nodes. From this infomation, we can establish what is called the Pathologic Stage.
Both the Clinical Stage and Pathologic Stage give us important pieces of information to help us decide on treatments. In many cases, we only have one or the other, and other tests of procedures may or may not be necessary to help figure out exactly what stage someone is at.