By staging a tumour, a clinician aims to gain an indication of the prognosis for an individual patient. The most commonly used system is TNM, but other staging systems (such as FIGO for gynaecological malignancies, and limited/extensive stage for small cell lung cancer) are also used.
General Principles of TNM Staging
TNM staging is determined on three factors:
- The extent of the primary tumour mass (T stage)
- The involvement and extent of regional lymph nodes (N stage)
- The presence of distant metastases (M stage)
The TNM staging system varies according to tumour site and occasionally histological type. It is regularly updated to account for advances in medical knowledge and diagnostic methods.
The TNM is primarily an anatomical staging system, although for some tumour sites it takes into account non-anatomical features. For example, the latest guidelines from the AJCC recommend using PSA and Gleason Score when determining the stage of prostate cancer.
The time at which staging is performed is also recognised by the TNM system. If a pathology specimen is used for staging, the symbol used is pT, pN or pM depending on the site. If staging is performed after therapy has occurred, an additional ‘y’ prefix is used.
The combination of T, N and M stage gives a final 'stage' of the disease, denoted by Roman numerals:
- Stage I is localised disease
- Stage II is early stage disease
- Stage III is locally advanced disease
- Stage IV is metastatic or otherwise incurable
A stage may be subdivided (eg. stage IIIa, IIIb, IIIc) when a global stage is inadequate.
General Principles of FIGO staging
FIGO staging is used for gynaecological malignancy. It has remained in favour due to dependence on clinical examination only, making it useful in third world countries where imaging is less available. Cervical cancer remains a very common malignancy in these countries. TNM staging can also be used for gynaecological staging.
FIGO staging has similar categories to TNM, from I - IV.
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