The term cancer is used for diseases in which abnormal cells divide without control, and can invade other tissues; in essence, a disruption in the regulation of growth of healthy cells occurs. Cells proliferate without normal organisation or normal control; cellular function becomes distorted, this is called carcinogenesis.
Cancer cells spread to other parts of the body through blood and lymph systems: this is known as metastases. The abnormal cells (the mutations) migrate from their original site invading nearby tissues and forming masses at distant sites of the body. Much progress related to unravelling the various steps associated with the processes related to carcinogenesis has occurred.
Cancer is a general term describing a group of related diseases. Every case of cancer is unique, with its own group of genetic changes and growth properties: it is essential to remember that the people who have cancer and their families are also unique. There are many main types of cancer. Cancer can be grouped into broader categories.
|
GROUP |
FORMATION |
EXAMPLE |
|
Carcinoma |
Cancer beginning in the skin or tissues that line or cover internal organs |
• Lung • Colon |
|
Sarcoma |
Cancer beginning in the bone, cartilage, fat, muscle, blood vessels or other connective or supportive tissue; these are rare |
• Kaposi’s sarcoma • Fibrosarcoma |
|
Leukaemia |
Cancer starting in the blood forming tissues such as the bone marrow, causes large numbers of abnormal blood cells to be produced; they then enter the blood stream |
• Acute lymphoblastic leukaemia • Chronic myeloid leukaemia |
|
Lymphoma |
Cancer beginning in the cells of the immune system |
• Non-Hodgkin lymphoma |
|
Central nervous system |
Cancers beginning in the tissues of the brain and spinal cord |
• Astrocytoma • Intramedullary tumour |
There are a number of other terms used to describe cancer, for example, malignancy, tumour, neoplasm.
THE NATURE OF CANCER
Cancer is not a single disease: it is an umbrella term.
• There are hundreds of different types and sub types of cancer affecting young and older people.
• Almost every tissue or organ in the body has the capacity to develop the disease.
• There is no age group, ethnicity or gender resistant to cancer; these features play a role in the incidence of some particular cancers, frequency and severity.
Cancer can have an overwhelming emotional and physical impact on the individual and is associated with significant complications (morbidity) and potential death (mortality).
Some cancers grow quickly; others can take years to become a threat to the patient. There are differences between cases of cancer, even of those of same organ (for example, different cases of breast cancer); this is one of the main reasons why treatment can be so difficult.
In spite of the differences between various types of cancer, all cancers share some common characteristics. It is necessary to understand the basic, shared, features of cancer as this will allow for an understanding of detection, diagnosis and the possible treatment options.
THE BIOLOGY OF CANCER
The development of cancer is a complex process involving the disruption of the regulation of the growth of normal cells. In order to begin to understand cancer it is important to appreciate normal cell growth and regulation. We are all made up of approximately a hundred million million (100,000,000,000,000) cells; there are over 200 various types of cells in the body. The cells cluster together forming tissue; tissues make up organs such as the breast, lung, prostate and colon.
Cells are formed from chemicals and other structures and found in all living matter. Almost all cells are microscopic, varying in size, shape and purpose. Cells are the building blocks of the body providing proper functioning for processes required to sustain life, for example, digestion, respiration, reproduction. This is a typical cell and its components:
Cellular components
Source: from Colbert, B.J., Ankey, J. and Lee, K.T. Anatomy and Physiology for Health Professionals. An Interactive Journey, 1st © 2007. Printed and electronically reproduced by permission of Pearson Education, Inc., Upper Saddle River, New Jersey.
At any one time the majority of cells in the body are not dividing, but they become stimulated to enter a cycle of division by growth factors or hormones (chemical messengers produced by the body, influencing the growth of certain cancers); this eventually results in the cell dividing into two daughter cells. Cells within different tissues are highly specialised and have a role to play, doing a specific job.
• Control of the cell cycle occurs through chemicals which combine with and activate enzymes.
• Some chemical messengers trigger a ‘braking’ action stopping the cycle from proceeding.
• There are a number of points during the cell cycle ensuring it proceeds in the right order. If there are any deviations, apoptosis (cell death) occurs.
• If there is a malfunction of any regulators of cell growth a division can result causing a rapid proliferation of immature cells.
CANCER CELLS
Normal body cells have a number of important characteristics. They can:
• reproduce themselves precisely
• stop reproducing at the right time
• remain together in the right place
• self-destruct if they become damaged
• become specialised or ‘mature’
Cells are said to be able to reproduce up to 50 or 60 times as a maximum, after this they die. Cancer cells are different: they do not die, they migrate to another part of the body, continuing to reproduce; for example, one cell becomes 2, then 4, and then 8, and then 16, and then 32 and so on:
• Cancer cells keep on doubling, irrespective of the damage the extra cells cause to the part of the body where the cancer is growing.
Cells forming tumour
Source: Macmillan Cancer Support
• Normal cells cease maturation once they have been made.
• Cancer cells do not specialise, but stay immature.
As a result of the rapid replication some of the genetic information in the cell can become lost and the cells become more and more unsophisticated with a tendency to reproduce faster and even more indiscriminately.
Differentiation
Cells usually become specialised during their development. All cells undergo an important adjustment during their lifetime, moving from unspecialised cells undergoing growth into specific cell types performing the responsibilities of specific tissues and organs: this is called differentiation – a less specialised cell becomes a more specialised cell. Cells originate from ‘stem’ cells; as the embryo grows, these cells differentiate, taking on different shapes in order to fulfil specific roles:
Cell differentiation
Source: The Center for Reproductive Sciences
Differentiation radically alters a cell’s size, shape, membrane potential, metabolic activity and the cell’s responsiveness to signals (usually hormonal signalling).
• If more than 75% of the tissue has altered this is poorly differentiated or undifferentiated; most of it has become altered and cancerous.
• If only 50% of the tissue has changed, this is moderately differentiated.
• If less than 25% has changed this is known as minimal differentiation.
This is important because it can help to determine how progressive the disease is; it also impacts on a person’s cancer diagnosis. The more the tissue has changed, the less likely it is to respond positively to cancer treatment.
SECTION SUMMARY
There are a variety of types of cells in the body and there are different types of cancer, arising from different types of cells. Cancers can arise from any tissue. What is important to understand is that usually there are notable differences between different types of cancer:
• some cancers develop and spread faster than others
• some are easier to treat than others, especially if they are diagnosed at an early stage
• some respond better than other cancers to chemotherapy, radiotherapy, or other treatments
• for some people there is a very good possibility of being cured; however, for others the outlook is poor
So, cancer is not just one condition. When caring for people with cancer it is essential to understand:
• what type of cancer has developed
• the size
• if there is any spread
• how well the specific type of cancer responds to the various types of treatments
Understanding cancer biology can often be daunting. You should spend a little more time in developing your understanding of cell biology, then relate this to cancer cell biology; this will help you feel more confident when caring for people with cancer.