Staging of cancer refers to classification of cancer by its anatomic disease extent, i.e, how large the tumor is, and if it has spread.
This staging system of cancer helps
- to express severity or extend of disease
- to estimate the prognosis of the disease
- provides useful information for treatment decision like planning, evaluation of results etc.
- facilitate the exchange of information between treatment centres
- contribute to continuing investigations of human malignancies
- support cancer control activities, including through cancer registries.
TNM (Tumor, Node, Metastasis) staging is the most widely used cancer staging system by most hospitals and medical centers. In TNM staging,
- The T refers to the size and extent of the main tumor. The main tumor is usually called the primary tumor.
- The N refers to the the number of nearby lymph nodes that have cancer.
- The M refers to whether the cancer has metastasized. This means that the cancer has spread from the primary tumor to other parts of the body.
Other classification systems used are WHO ICD-O, Tanis score and SNOMED systems. But these are less popular than TNM staging.
History of TNM Staging
TNM Staging was first developed by Pierre Denoix between 1943-52. The first cancers to be staged using this system were laryngeal and breast cancer, in Europe by the UICC (International Union against Cancer).
The first TNM booklet (Livre de poche) was published a decade later. The AJCC-ER (American Joint Committee for Cancer Staging and End Results Reporting) revised and started implementing this from mid-1970. The current version of AJCC staging system is based on the AJCC Cancer Staging Manual (8th ed.). 2016.
Principles and General rules of TNM Staging
TNM staging is based on the principle that, an orderly progression of disease takes place with enlargement of and invasion by primary tumor (T), followed by spread to regional lymph nodes (N) and eventually spread beyond nodes to distant sites (M).
In TNM Staging,
- T refers to the extend of primary Tumor
- N refers to absence/presence and extend of regional lymph node metastasis
- M refers absence/presence of distant metastasis.
- The individual TNM classifications are then assembled into 4 groups – stage groups I-IV.
- c: stage is determined before treatment based on informations available from clinical examination, imaging, endoscopy, biopsy and surgical exploration. The c-prefix is implicit in absence of the p-prefix.
- p: stage determined after surgery or by histopathologic examination of a surgical specimen
- y: stage assessed after chemotherapy and/or radiation therapy; in other words, the individual had neoadjuvant therapy.
- r: stage for a recurrent tumor in an individual that had some period of time free from the disease.
- a: stage determined at autopsy.
- u: stage determined by ultrasonography or endosonography. Clinicians often use this modifier although it is not an officially defined one.
- When sentinel LN biopsy is attempted, a suffix ‘SN’ after N stage is done.
- Absence/presence of residual tumor after treatment may be described by symbol R.
- AJCC recommends each N staging category to record and show whether the nodes are involved in upper (U) or lower (L) region of neck – depending on their location above or below lower border of thyroid cartilage.
- The number of nodes that contain Tu and presence or absence of extracapsular spread of Tu also needs to be documented.
TNM Staging of Head & Neck cancers
Strengths & Limitations of TNM staging
The simplicity of classification, the low cost, relative accuracy, objectivity, universal acceptance and lack of need for special technology are the strengths of TNM staging.
The limitations of TNM staging include
- Inter observer variability
- Differences in staging methods.
- TNM is not intuitive and need a chart for most surgeons to stage their patients.
- The current TNM system relies on tumor morphology with little or no attention to patient factors.
- No consideration for severity and co-morbidity.
- Limitations of T staging
- T stage per se doesn’t influence prognosis.
- Size of tumor is not always easily measurable.
- Difficulty in classification when tumor size is borderline (between 1.5-3cm).
- Discrepancies when tumors are classified according to number of anatomical subsites involved especially in laryngeal cancer.
- Tumor of hypopharynx especially marginal zone/aryepiglottic fold classification is controversial.
- Limitations of N staging
- Interobserver variations on their presence.
- Palpable nodes mayn’t be always metastatic.
- Retropharyngeal nodes are excluded.
- Doesn’t allow independent classification of massive nodes on both sides of neck, which are often fixed and almost fatal.
- During clinical examination and measurement using caliper, the intervening soft tissue thickness needs to be considered.
- Most masses over 3cm in diameter are not single nodes, but represents confluent nodes or tumor in for tissue compartment of neck.
- The original TNM staging lacks description of level of nodal involvement which was later corrected by integrating Memorial-Sloan Katering LN level systems.
- Limitations of stage grouping
- Size of some groups defined by the combinations of TNM classifications is small, preventing accurate prediction from previous experience.
- 8th Edition of the UICC TNM classification of Malignant Tumors published
- Gospodarowicz MK, Brierley JD, Wittekind C, editors. TNM classification of malignant tumours. John Wiley & Sons; 2017 Jan 17.
- Lydiatt WM, Patel SG, O’Sullivan B, Brandwein MS, Ridge JA, Migliacci JC, Loomis AM, Shah JP. Head and neck cancers—major changes in the American Joint Committee on cancer eighth edition cancer staging manual. CA: a cancer journal for clinicians. 2017 Mar 1;67(2):122-37.