Stages of Cancer
Several cancer-staging systems have been developed to describe the extent that a cancer has spread. Staging is important because it is used to determine a patient’s treatment and prognosis. The patient’s overall health, as well as their sensitivity to certain medications and tests will also influence their ultimate treatment and prognosis.
Staging is used to describe almost every cancer type, except for leukemia. Leukemia, a disease of the blood, is not anatomically localized like other cancers. Therefore, it is impossible to describe how far the disease has “spread”. Staging systems have been designed to complement the unique characteristics of certain leukemias, but as a whole, the disease cannot be staged.
Staging Systems Explained
Overall Stage Grouping
This staging system, commonly referred to as Roman Numeral Staging, is used to describe the progression of most cancers. Roman numerals I, II, III, and IV (with the occasional inclusion of the 0) are used to identify increasing levels of cancer spread:
- Stage 0: This stage is referred to as carcinoma in situ, derived from the Latin phrase meaning “in its place”. These extremely early-stage cancer cells divide in their normal habitat. For example, Stage 0 skin cancer cells would not divide beyond the boundaries of the epidermis. Most cancers at this stage are highly treatable.
- Stage I: These cancers are localized to one part of the body.
- Stage II: These cancers are considered “locally advanced”. This means that they have spread or invaded beyond the boundaries of their original habitat. Depending on the cancer, Stage II may be used to indicate a variety of characteristics.
- Stage III: In a general sense, Stage III also describes “locally advanced cancers”. Depending on the cancer, the term Stage III is used to describe characteristics that are similar, but more advanced than Stage II characteristics.
- Stage IV: These cancers have spread to other locations throughout the body.
TNM staging is a system used to describe the characteristics of solid tumors. The acronym represents the following terms: Tumors, Nodes, and Metastasis.
- T: T is used to describe the primary tumor. It is assigned numbers 0 through 4 (appearing as T0 through T4). These four numbers correlate with the four Roman numerals of the Overall Staging System.
- N: N identifies the extent of regional lymph node involvement. This descriptor is also assigned numbers 0 through 4, indicating lymph node involvement in increasing levels of severity. An N0 cancer, for example, has no regional lymph node involvement. An N4, on the other hand, indicates extensive involvement. The N descriptor does not identify the involvement of distantly located lymph nodes. This type of involvement would be classified as metastasis.
- M: M is assigned the numbers 0 and 1. M1 identifies a cancer with no metastasis, and M1 identifies a cancer that has metastasized (spread) to other locations throughout the body.
A lowercase ‘c’ or ‘p’ is used in the TNM system to denote whether a cancer is in the clinical or pathologic stage.
- Clinical Stage: Clinical stage cancers are identified using all of the information that isprocured before the surgical removal of the tumor. This information may include the results of a physical examination and certain imaging tests.
- Pathologic Stage: The identity of pathologic stage cancers has been embellished by the addition of information gained through histological (microscopic) evaluation of tissue samples.
Using the TNM system, a patient with a ‘cT1N0M0’ cancer would have a clinical stage T1 tumor with no lymph node involvement and no metastasis.
Staging System Variations
Not all cancers can be appropriately divided into four categories. As a result, the four Roman numeral descriptors of the Overall Staging System are often divided into subcategories designed to complement the unique characteristics of certain cancers. For example, lung cancer stage IIIa usually necessitates a completely different treatment strategy than stage IIIb lung cancer. Although, they are similarly “locally advanced”, the ‘a’ and ‘b’ variations of stage III lung cancer are very important descriptors for the treatment and prognosis of the disease.
Because leukemia is a disease of the blood, descriptors that identify cancer location and spread simply do not apply. Blood circulates throughout the entire body. It wouldn’t make sense to describe a leukemia as having spread to the chest, for example.
The Roman numerals I through IV are sometimes used to describe the features of a certain type of leukemia and/or the onset of symptoms. But these numerals cannot be used to describe all leukemias.
Why ‘Standard’ Terminology Isn’t Standard
Certain cancers, such as prostate and colon cancers, may be identified with the letters A through D, or a completely different set of letters, numbers, and characters. Furthermore, these “alternative” systems are often used in addition to the Roman numeral system. It is important to be aware of which staging system is being used to describe your cancer, and how that system might pertain uniquely to your condition.
As if the staging of cancer weren’t confusing enough, the various descriptors of a cancer are regularly revised as new treatment options are developed and new information is gathered through research. This process is known as stage migration.
Remember, Staging Isn’t Everything
Although staging is an important indicator of how a cancer should be treated, it cannot foretell the end result of a patient’s battle with cancer. Know Cancer’s very own co-founder, Joshua Snyder, was diagnosed with Stage IV Hodgkin’s lymphoma. He is now cancer-free.