CANCER STAGING

In September, 2018, I published a lengthy article titled “Cancer: A Diagnosis Everyone Fears.” On page 3 of the essay I wrote about cancer staging and its significance to surgeons and oncologists. Staging is important for determining treatment protocols and for prognostic expectations. Staging is determined by a compilation and organization of the data obtained from all the diagnostic tests performed.  

Most physicians use a numeric staging system for simplicity and consistency. For example, if every physician uses the same system for every cancer diagnosis, any treating doctor will know what is meant by the stage reported. There are different staging systems for different cancers. Brain, spinal cord, prostate, and blood cancers have systems specific to their diagnosis. Specialists within the fields of these diagnoses become familiar with the staging for the cancer they treat. 

The lay public has developed familiarity with the system using five stages, 0, 1, 2, 3, 4. The more frequently diagnosed cancers use this system because it is much simpler and easy to understand. On the other hand, cancer surgeons and many oncologists use the “TNM” system. The TNM system can be adapted to the “0-4” system rather easily. An explanation of the two major staging systems will now follow. I think you will quickly see why the “0-4” system lends itself to acceptance much more readily. 

Stage 0,1, 2, 3, 4: After completion of blood tests, imaging studies, and needle or open biopsies, one of the stages fits. The stages are:

STAGE 0–stands for abnormal looking, pre-cancerous cells on the surface layer of the tissue, stands for carcinoma in situ. 

STAGE 1–cancer is present but confined to only one site.

STAGE 2–cancer has spread from the site of origin to deeper, wider layers, ie. local extension

STAGE 3–cancer has spread to adjacent tissues outside the site of origin or to regional lymph nodes-ie. local metastases.

STAGE 4–cancer has spread to distant organs (lungs, liver, bone, brain)—ie. distant metastases

From this system, patients and families are quite aware of the seriousness of a Stage 3 or Stage 4 cancer. The higher the stage number, the more advanced is the cancer. The prognosis, regardless of organ or cell type, is very poor. The system is specific enough for most oncologists and the lay public.

The other commonly used cancer staging system is the “TNM” system. The system is more specific in its quantization and location of the cancer. From this system, doctors get a better notion of the extent and location of the cancer in the body. This system provides information on the location of the primary tumor, it’s size and extent, if there is lymph node involvement, and if distant metastases are present. T represents TUMOR, N represents LYMPH NODES, and M means METASTASES. 

The T Category describes the original TUMOR: Subcategories describe extent of tumor.

     TX means there is no information on the primary tumor, or it can’t be measured.

     T0 means there is no evidence of primary tumor (it cannot be found).

     Tis means cancer cells are growing only in the surface layer of the tissue.

     T1,2,3,4 describes the primary tumor size and extent of local growth.

The N category describes what her or not the cancer has reached nearby lymph nodes

     NX means regional lymph nodes cannot be evaluated.

     N0 means there is no regional lymph node involvement

     N1,2,3 means regional nodes are cancerous and the extent thereof.

The M category tells whether there are distant metastases (spread to other parts of body)

     M0 means no distant metastases

     M1 means cancer has spread to distant parts of the body (liver, lung, brain, bone)

Because each cancer type has its own “TNM” classification, the Stage 0-4 system is used to clarify and simplify, with less specificity, the extent of cancer involvement. A lot of investigation goes in to determining the stage of a cancer. These blood, imaging, and biopsy results are all taken into account when staging is determined. It takes a lot of data to make the determination, but staging does have therapeutic and prognostic significance. It is far more easily understood when T4,N3,M1 is replaced with Stage 4. Everyone knows what Stage 4 means, but TNM staging requires a reference standard. Unfortunately, prognostically and therapeutically they have the same meaning, just in a simpler format. 

To better understand cancer staging, a few examples follow: 

     A colon polyp with a few cancerous cells in the surface layer of the tip: Stage 0

     A cancerous colon lesion that extends to the outer surface of the colon and found in lymph

          nodes nearby: Stage 3

     A cancerous tumor in the colon with known liver metastases: Stage 4

Pathologists, oncologists, and surgeons use these classifications every day to help them know how best to treat the patient, what is the appropriate treatment protocol, and what to tell the patient and family about the future. 

References: Groome PA, et al. The IASLC Lung Cancer Staging Project: validation of the proposals for revision of the T, N, M descriptors and consequent stage groupings in the forthcoming edition of the TNM classification of malignant tumors. Thorac Oncol 2007 Aug;2(8):694-705.

https://www.facs.org/quality-programs/cancer-programs/american-college-of-surgeons/cancer-staging/