Neoplasms definition
A tumour or neoplasm is a mass of tissue that grows faster than normal in an uncoordinated manner, and continues to grow after the initial stimulus has ceased.
Neoplasms can be classified as
They are consists of the two terms-
- Benign Tumour
- Malignant tumour
Tumours are classified as benign or malignant although a clear distinction is not always possible. Benign tumours only rarely change their character and become malignant. Tumours, whether malignant or benign , may be classified according to their tissue of origin, e.g. adeno-, sarco-, the letter may be further distinguished e.g. myo-, osteo-. Malignant tumour are further classified according to their origins; for example, a carcinoma, the commonest form of malignancy, originates from epithelial tissue and a sarcoma arises from connective tissue. Hence, an adenoma is a benign tumour of glandular tissue but an adenocarcinoma is a malignant tumour of the epithelial component of glands; a benign bone tumour is an osteoma, a malignant bone tumour an osteosarcoma.
Neoplasms causes
There are more than 200 different types of cancer, but all are caused by mutation within the cell's genetic material. Some mutation are spontaneous, i.e. happen by chance during cell devision, other are related to exposure to a mutagenic agent and a small proportion are inherited. Advancing knowledge in the area has led to identification of many specific genes/chromosomes mutation associated directly with particular cancers. Cell growth is regulated by gene that inhibit cell growth and genes that stimulate cell growth. One important tumour suppressor gene, is thought to be defective in 50-60% of cancers. A proto-oncogene that become abnormally activated and allows uncontrolled cell growth can also cause cancers and is then referred to as an oncogene.
Carcinogene
These cause malignant changes in cells by irreversibly damaging a cell's DNA. It is impossible to specify a maximum 'safe dose' of a carcinogen. A small dose may initiate change but this may not be enough to cause malignancy unless there are repeated doses over time that have a cumulative effect. In addition, there are widely varying latent periods between exposure and signs of malignancy.
Chemical carcinogens
Example include:- Cigarette smoke, which is the main risk factor for lung cancer.
- Asbestos, which is associated with pleural mesothelioma.
Ionising radiation
Exposure to ionising radiation including X-rays, radioactive isotopes, environmental radiation and ultraviolet rays in sunlight may cause malignant changes in some cells and kill others. Cells are affected during mitosis so those normally undergoing frequent division are most susceptible. These labile tissue include skin, mucous membrane, bone marrow, reticular tissue and gametes in the ovaries and testes. For example, repeated episodes of sunburn predispose to development of skin cancer.
Oncogenic cancer
Some viruses cause malignant changes. Such viruses enter cells and incorporate their DNA or RNA into the host cell's genetic material, which causes mutation. The mutant cells may be malignant. Example include hepatitis B virus, which can cause liver cancer and human papiloma virus (HPV) which is associated with cervical cancer.
Host factors
Individual characteristics can influence susceptibility to tumours. Some are outwit individual control e.g. race, increasing age and inherited factors. Others can be modified and are referred to as lifestyle factor ; these include eating a healthy balanced diet, cigarette smoking, taking sufficient exercise and avoiding obesity. Making healthy lifestyle choices where possible is important as these factors are thought to be involved in the development of nearly half of all malignant tumours.
Growth of tumours
Normally cells divide in an orderly manner. Neoplastic cells have escaped from the normal control and multiply in a disorderly and uncontrolled manner forming a tumour. Blood vessels grow with the proliferating cells, providing them with a good supply of oxygen and nutrients that promote their growth. In some malignant tumours the blood supply does not keep pace with growth and ischaemia death. If the tumour is near the body surface, this may result in skin ulceration and infection. In deeper tissues there is fibrosis; e.g. retraction of the nipple in breast cancer is due to the shrinkage of fibrous tissue in a necrotic tumour.
Cell differentiation
Differentiation into socialised cell types with particular structural and functional characteristics occurs at an early stage in feel development, eg. epithelial cells develop different characteristics from lymphocytes. Later, when cell replacement occurs, daughter cell have the same appearance, functions and genetic make-up as the parent cell. In benign tumours the cells from which they originate are easily recognised, i.e. tumour cells are well differentiated. Tumours with well-differentiated cells are usually benign but some may be malignant.
Encapsulation and spread of tumours
Most benign tumours are contained within a fibrous capsule derived partly from the surrounding tissues and partly from the tumour. They neither invade local tissues nor spread to other parts of the body, even when they are not encapsulated.
Malignant tumour are not encapsulated. They spread locally by growing into and infiltrating nearby tissue.tumour fragments may spread to other parts of the body in blood or lymph. Some of the spreading tumour cells may be recognised as 'non-self' and phagocytosed by macrophages or destroyed by defence cells of the immune system, e.g. cytotoxic T-cells and natural killer cells.
Local spread
Benign tumour enlarge and may cause pressure damage to local structure but they do not spread to other parts of the body.
Benign or malignant tumour may:
- Damage nerves, causing pain and loss of nerve control of other tissues and organ supplied by the damaged nerves
- Compress adjecent structures causing e.g. ischaemia, necrosis, blockage of ducts, organ dysfunction or displacement, or pain due to pressure on nerves.
Body cavities spread
This occurs when a tumour penetrates the wall of a cavity. The peritoneal cavity is most frequently involved. If , for example, a malignant tumour in an abdominal organ invade the visceral peritoneum, tumour cells may metastasise to folds of peritoneum or any abdominal or pelvic organ. Where there is less scope for the movement if fragments within a cavity, the tumour tends to bind layers of tissue together, e.g.a pleural tumour binds the visceral and parietal layers together, limiting expansion of the lung.
Lymphatic spread
This occurs when malignant tumours invade nearby lymph vessels. Groups of tumour cells break off and are carried to lymph nodes where lodge and may grow into secondary tumours. There may be further spread through the lymphatic system and to blood because lymph drains into the subclavian veins.
Effects of tumours
Pressure effects
Both benign and malignant tumours may compress and damage adjacent structures, especially if in a confined space. The effects depend on the site of the tumour but are most marked in areas where there is little space for expression, e.g. inside the skull, under the periosteum of bones, in bony sinuses and respiratory passage. Compression of adjacent structures may cause ischaemia, necrosis, blockage of ducts, organ dysfunction or displacement, pain due to invasion of nerves or pressure on nerves.
Hormonal effect
Tumours of endocrine glands may secrete hormones, producing the effects of hypersecretion. The extent of cell dysplasia is an important factor. Well-differentiated benign tumours are more likely to secrete hormones than markedly dysplastic malignant tumours. High level of hormones are found in the bloodstream as secretion occurs in the absence of the normal stimulus and homeostatic control mechanism. Some malignant tumours produce uncharacteristic hormones, e.g. some lung tumours produce insulin. Endocrine glands may be destroyed by invading tumours, causing hormone deficiency.
Causes of death in malignant disease
Infection
Acute infection is a common cause of death when superimposed on advanced malignancy. Predisposition to infection is increased by prolonged immobility or bedrest, and by depression of the immune system by cytotoxic drugs and radiotherapy or radioactive isotopes used in treatment. The most common infections are pneumonia, septicaemia, peritonitis and pyelonephritis.
Organ failure
A tumour may destroy so much healthy tissue that an organ cannot function. Severe damage to vital organs, such as lungs, brain, liver and kidneys, are common cause of death.
Carcinomatosis
This is the presence of widespread metastatic disease and is usually associated with cachexia. Increasingly severe physiological and biochemical disruption follows causing death.
Haemorrhage
This occurs when a tumour grows into and ruptures the wall of a vein or artery. The most common sites are the gastrointestinal tract, brain , lungs and the peritoneal cavity.
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