CANCER STAGING / STAGES OF CANCER 

The stage of a cancer is a descriptor (usually numbers I to IV) of how much the cancer has spread. The stage often takes into account the size of a tumor, how deep it has penetrated, whether it has invaded adjacent organs, how many lymph nodes it has metastasized to (if any), and whether it has spread to distant organs. Staging of cancer is important because the stage at diagnosis is the most powerful predictor of survival, and treatments are often changed based on the stage.

Cancer staging can be divided into a clinical stage and a pathologic stage:
• Clinical stage is based on all of the available information obtained before a surgery to remove the tumor. Thus, it may include information about the tumor obtained by physical examination, radiologic examination, and endoscopy.
• Pathologic stage adds additional information gained by examination of the tumor microscopically by a pathologist.

Pathologic staging is usually considered the "better" or "truer" stage because it allows direct examination of the tumor and its spread. However, not every tumor is treated surgically, so sometimes pathologic staging is not available. Thus, clinical staging and pathologic staging should complement each other.

Correct staging is critical because treatment is directly related to disease stage. Thus, incorrect staging would lead to improper treatment, and material diminution of patient survivability. Correct staging, however, can be difficult to achieve. Pathologic staging, where a pathologist examines sections of tissue, can be particularly problematic for two specific reasons: visual discretion and random sampling of tissue.

New, highly sensitive methods of staging are in development. For example, the mRNA for GCC (guanylyl cyclase C), present only in the luminal aspect of intestinal epithelium, can be identified using molecular screening (RT PCR) with an astonishing degree of sensitivity and exactitude. Presence of GCC in any other tissue of the body represents colorectal metaplasia. Because of its exquisite sensitivity, RT PCR screening for GCC nearly eliminates the possibility of underestimation of true disease stage. Researchers hope that staging with this level of precision will lead to more appropriate treatment and better prognosis. Furthermore, researchers hope that this same technique can be applied to other tissue-specific proteins.

Overall Stage Grouping is also referred to as Roman Numeral Staging. This system uses numerals I, II, III, and IV (plus the 0) to describe the progression of cancer.
• Stage 0 carcinoma in situ i.e. the malignant cells have not yet invaded the deeper epithelial tissue or spread to other parts of the body.
• Stage I (stage 1) cancers are localized to one part of the body.
• Stage II cancers are locally advanced, as are Stage III cancers. Whether a cancer is designated as Stage 2 or Stage 3 can depend on the specific type of cancer; for example, in Hodgkin's Disease, Stage II indicates affected lymph nodes on only one side of the diaphragm, whereas Stage III indicates affected lymph nodes above and below the diaphragm. The specific criteria for Stages II and III therefore differ according to diagnosis.
• Stage IV (stage 4) cancers have often metastasized, or spread to other organs or throughout the body.

TNM Staging is used for solid tumors, and is an acronym for the words Tumor, Nodes, and Metastases. Each of these criteria is separately listed and paired with a number to indivate the TNM stage. A T1N2M0 cancer would be a cancer with a T1 tumor, N2 involvement of the lymph nodes, and no metastases (no spreading through the body).
• Tumor (T) refers to the primary tumor and carries a number of 0 to 4.
• N represents regional lymph node involvement and can also be ranked from 0 to 4.
• Metastasis is represented by the letter M, and is 0 if no metastasis has occurred or 1 if metastases are present.

Within the TNM system, a cancer may also be designated as recurrent, meaning that it has appeared again after being in remission or after all visible tumor has been eliminated. Recurrence can either be local, meaning that it appears in the same location as the original, or distant, meaning that it appears in a different part of the body.