Tonks N. Fawcett, BSc (Hons), MSc, RN, RNT, ILTM
LecturerUnlike normal cells, cancer cells are not subject to the usual restrictions placed by the host on cell proliferation (Pfeifer, 1997). However, cell proliferation is not always indicative of cancer and new growths, or neoplasms, may be either benign or malignant. A benign neoplasm is seen as 'strictly a local affair' (Marieb, 1998). The cells do not spread to other parts of the body and so are not defined as cancerous. A malignant neoplasm, by contrast, consists of cancer cells that have the ability to spread beyond the original site.
Unlike normal cells, cancer cells are not subject to the usual restrictions placed by the host on cell proliferation (Pfeifer, 1997). However, cell proliferation is not always indicative of cancer and new growths, or neoplasms, may be either benign or malignant. A benign neoplasm is seen as 'strictly a local affair' (Marieb, 1998). The cells do not spread to other parts of the body and so are not defined as cancerous. A malignant neoplasm, by contrast, consists of cancer cells that have the ability to spread beyond the original site.
A common misconception is that a cancer is a population of cells that reproduces much faster than normal cells. More accurately, tumours consist of mixtures of non-dividing, resting and continuously dividing cells (Pfeifer, 1997). All malignant neoplasms contain cells that are not subject to the normal restraints on cell proliferation, leading to cell growth beyond normal margins. This abnormal growth exerts pressure on other organs and leads to the tendency for cancer cells to invade neighbouring tissues and structures (Pfeifer, 1997). Cell numbers increase exponentially in powers of two, and the time needed for a tumour to double its volume is known as its doubling time (DT). Because tumour cells divide at different times, the growth fraction (GF) - the ratio of the total number of cells to the number of proliferating cells - is an important concept in the determination of DT and provides a means whereby the proliferate capacity of a tumour can be estimated (Pfeifer, 1997).
During metastasis, cancer cells trespass aggressively into other tissues (Ruoslahti, 1996). Acquiring the ability to migrate to another tissue is a key event in the development of cancer (Ruoslahti, 1996). The process that a cell must undergo to form a metastasis is complex, involving escape from the primary tumour, movement to a new location and establishment of growth at the new site, a process known as the metastatic cascade. Metastatic cells usually travel in the lymphatic system or the bloodstream (Gribbon and Loescher, 2000). Metastases may be located in different organs and in different regions of the same organ. The organs commonly invaded by metastases are the lungs, bones, brain, liver and lymph nodes. However, the pattern of metastatic spread is not random and certain tumours 'favour' colonising particular sites for metastatic growth (Alison and Sarraf, 1997).
The classification of cancer
As indicated, cancer is a collection of diseases with certain common features. Patients often view cancer as a single disease and use the term generically (Varmus and Weinberg, 1993). The difficulty with such a generic term is that it is loaded with meanings for people and these are inevitably negative. There are, in fact, more than 200 different types of cancer (Souhami and Tobias, 1995). All cancers begin as an individual cell and because each cell in the body is unique, each cancer is also unique (Morgan, 2001). Any tumour may be classified by a behaviouristic classification and/or the histogenic classification.
Behaviouristic classification - The greatest distinction between tumour types depends on the degree of malignancy. Both truly benign and truly malignant tumours exist. There are, however, benign tumours that predispose to malignant change, such as adenomas of the large intestine, and there are some in situ carcinomas that progress so slowly that they never achieve malignancy, such as certain in situ carcinomas of the uterine cervix. Thus, a spectrum of types of tumour behaviour exists.
Histogenic classification - The most widely employed classification of tumours is based on their histogenesis and defines a tumour according to the tissues or cells from which it arises (Gowing and Fisher, 1988). Thus malignant neoplasms can be described as carcinomas (cancer of the epithelial cells), sarcomas (cancer of connective tissue) and leukaemia (cancer of white blood cells) (Morgan, 2001).
Grading malignant tumours
Types of cancer cells making up a tumour can also be graded according to their degree of malignancy, further illustrating the complexity of the condition. Grading is based on the histopathological characteristics of the tissue and assesses the aggressiveness, or degree of malignancy, of the cells by comparing the cellular anaplasia, differentiation, and mitotic activity against those of their normal counterparts (O'Mary, 1993). Specific characteristics vary with each type of cancer.
Tumour grading helps with planning treatment and determining prognosis (O'Mary, 1993). The Union Internationale Contre le Cancer (UICC) recommends that primary tumours are graded and recorded under the system shown in Box 1 (O'Mary, 1993). Certain problems exist with grading classifications as a tumour's level of differentiation may vary with time and it is also possible for several grades of malignancy to exist within one tumour. Patients rarely have knowledge of the specific grading of their tumour cells but a greater understanding of the grading would enable patients to have a better insight into how their particular tumour will be treated and what to expect in terms of disease progression.
Staging the extent of the cancer
Staging is a system used to establish, at presentation, the extent of the disease and is one aspect of the identification of factors that will influence prognosis in any individual patient (Neal and Hoskin, 1994). Staging is a clinical and histological determination that depends on the natural course of each particular type of cancer (O'Mary, 1993) and once a diagnosis of malignancy has been confirmed, the stage of the cancer must be ascertained. A number of international agencies have developed ways of staging the different cancers. The Tumour, Node, Metastases (TNM) system, however, remains the most widely used (Box 2). It has the virtue of simplicity, drawing attention to the prognostic relevance of the size or local invasiveness of the primary tumour (T), lymph node spread (N) and the presence of distant metastases (M) (Souhami and Tobias, 1995).
Staging is essential for the selection and evaluation of the therapeutic interventions and also provides the most precise data from which to estimate prognosis and calculate outcomes (Sobin and Wittekind, 1997). Patients tend to be given information regarding staging either by the medical and nursing staff or may read about staging in the various patient-information leaflets or websites available. Knowledge of the stage of a patient's cancer helps answer prognostic questions in terms of not only the proposed treatment but also, more crucially, of the likely outcome (Hamilton, 1994).
- See also the March 2002 article by Drew, A., Fawcett, T. Responding to the information needs of patients with cancer. Professional Nurse 17: 7, 443-446.
A young male patient is undergoing investigations for a testicular lump. How would you answer if he asked you the difference between benign and malignant tumours? What particular communication skills might facilitate sensitivity in your response?
What do the terms 'carcinoma in situ' and 'invasive carcinoma' mean? Drawing on the references given above, describe in more detail the metastatic spread that may occur.
Tumour classification is considered by Alison and Sarraf (1997) to be far from satisfactory. Look at the various classifications of malignant tumours and consider for yourself why this might be the case.
Why might a patient not know the grading of his or her tumour?
Reflect on the patients for whom you have cared who had a diagnosis of cancer. How much do you believe patients wish to know about the biology of their cancer? On what evidence do you base your view?
- This educational hand-out can be photocopied and used in teaching sessions on this subject.
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Pfeifer, K.A. (1997)Pathophysiology (chapter 1, unit 1). In: Otto, S.E. (ed.). Oncology Nursing (3rd edn). St.Louis, Mo: Mosby.
Ruoslahti, E. (1996)How cancer spreads. Scientific American 275: 3, 42-48.
Sobin, L.H., Wittekind, C.H. (1997)TNM Classification of Malignant Tumours (5th edn). New York, NY: Wiley-Liss.
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Varmus, H., Weinberg, R. A. (1993)Genes and the Biology of Cancer. New York, NY: Scientific American Library.