After a diagnosis of cancer has been made, the person undergoes a series of investigations to determine the characteristics of the tumour tissue and the extent of spread of disease in the body. This process, known as disease staging, is generally commenced before treatment begins.
The information gathered from staging investigations is used to classify a tumour and, based on accumulated evidence on the clinical behaviour of other tumours with similar characteristics, guides treatment planning and estimations of disease prognosis.37, 38
Histopathological review, the microscopic examination of tumour tissue, allows the identification of a number of properties that will enable assessment of a tumour's aggressiveness. The amount of necrosis, inflammation, haemorrhage, cellular genetic changes and the degree mitotic activity within a tumour tissue specimen are some of the properties examined in the laboratory. These histopathological characteristics are used to categorise a tumour into a grade, ranging from well-differentiated (grade 1), through moderately (grade 2) and poorly differentiated (grade 3) to undifferentiated (grade 4). In general, higher grade tumours are more aggressive and carry a worse prognosis than lower grade malignancies.37, 38, 42
In addition to classifying a cancer on the basis of histopathological characteristics, it is also usual to classify a malignancy on the basis of the anatomical extent of disease. Once again, extensive observation of the clinical behaviour of cancers allows prediction of the natural history of growth and progression of a cancer.
Information gathered from tests conducted during the process of cancer diagnosis, often referred to as staging investigations, can be used to compare a newly diagnosed cancer to similar cases and make predictions about the potential outcomes of treatment. In general, the greater the anatomical extent of the cancer, the more limited the successful treatment options and the poorer the prognosis becomes.30, 38
The tumour-node-metastasis (TNM) staging system
One of the most commonly used staging systems for solid tumours such a breast, lung and colon cancers, is the tumour-node-metastasis or TNM system. The TNM system, used internationally, is regularly reviewed to incorporate changing knowledge about the behaviour of tumours. The system assesses and classifies three properties:
- the extent of the primary tumour (T)
- the presence and extent of lymph node involvement (N)
- the presence of metastases (M).
Numerical values are assigned to various levels within each of the three categories, reflecting increasing extent of disease. The summing of the numerical values for each of the three categories allows the tumour to be classified into one of four stages, numbering stage I through to stage IV. High stage disease (stage III or IV) reflects greater anatomical extent and is correlated with poorer prognosis.
There are also a number of other staging systems, devised by the interest groups of oncology clinicians that are used together with or instead of the TNM system. Each of these systems defines the clinical aspects of particular cancers that correlate with favourable and unfavourable outcomes and are used to guide treatment decisions.30, 37, 38
Access a current text and/or the National Cancer Institute web site – Tumor Grade43 and prepare a brief explanation of the term high grade tumour for a person affected by cancer.
Access a current text or website (such as cancer.gov44) and compare the methods of staging lung and breast cancers.