Neoplasia
Neoplasia
" New Growth" = Growth of a tissue by cell multiplication outside the needs of normal function and showing little or no response to normal mechanisms which regulate cell division
Tumours
Neoplastic structures which may be composed of one or more tissue types.
Carcinogens
Agents which promote the initiation of neoplasia.
Prognosis
The outlook for cure / survival
Mean survival time
The average time which patients suffering from a particular condition survive.
Neoplasia results from unchecked cell replication which itself results from DNA faults.
Types of carcinogen
1) Chemical- chemical carcinogens may be found naturally in the environment (e.g. nitrates in food can promote alimentary cancer). They may be man-made or artificially produced (e.g. organic solvents, petrol, multiple chemicals in cigarettes), and they may be substances produced by other organisms, ( e.g. Helicobacter infection in the stomach can lead to ulcers and then cancer).
2) Radiation
High energy radiation such as X-rays and that from nuclear sources can damage DNA. Ultraviolet radiation from the sun can cause problems for white cats, and some collies with pale noses.
3) Genetic. Not strictly a carcinogen, but there is a genetic predisposition to many cancers which explains why not all animals will develop the same tumours under the same circumstances.
Tumours are divided into benign and malignant types.
Benign
Do not spread to sites distant to the primary tumour.
Malignant
Do spread to other sites. Malignant spread is via the blood stream or lymphatic ducts, cells lodge in the nearest narrow tube, usually where there are capillaries, and tumours grow from these cell colonies. Cells also spread by crossing body cavities in fluids (exfoliation), so this type of spread is seen in the abdomen, thorax, and brain. This spread is called Metastasis.
BUT some malignant tumours respond to therapy relatively well, whereas some benign tumours are virtually impossible to remove either because of their position or because they send tendrils of cells deep into local tissues, rendering removal of an adequate margin impossible. Also some benign tumours may have other effects on the body (e.g. Thyroid adenomas in cats are benign but can secrete large amounts of thyroid hormone).
Some Common Tumour Types
-Haemangiosarcomas are found in spleen and liver. They are malignant blood vessel tumours, and occur in dogs, mainly large breeds.
-Mammary tumours are often mixed tissue tumours of the mammary glands. They occur in dogs (50% benign), cats (90% malignant), and small rodents, particularly rats (99% malignant).
-Adenomas are benign tumours from secretory tissue, so they are glandular. Common adenomas are Perineal adenoma - found in the perineum of male dogs , sebaceous adenoma- found in the skin of dogs, thyroid adenoma- found in cats.
-Adenocarcinomas are malignant forms of the adenoma.They also occur in secretory tissue, e.g. bronchial adenocarcinoma in dog and cat lungs. In rabbits, early spaying is now recommended to prevent uterine adenocarcinoma, which is common in older females.
-Lipomas are benign fatty tumours under the skin. They occur mainly in dogs, but quite large ones are also commonly found in budgerigars.
-Melanomas may be malignant or benign depending on site. Skin melanomas in pets are usually benign, except in mice and gerbils. Oral melanomas are seen in dogs mainly, but also cats and are malignant.
-Papillomas are benign skin "warts" seen in dogs.
-Squamous cell carcinoma is a skin tumour which is benign in its early stages, but then becomes malignant. This is a tumour of the ear tip and nose , mainly in white haired cats. Because it can be cured if caught early, it should be watched for.
-Osteosarcomas are very malignant bone tumours, mostly in dogs.
-Lymphomas and lymphosarcomas are malignant tumours of the lymphatic system, found in dogs and cats. Cats are often FeLV positive.
Diagnostic techniques
Sometimes Imaging will be very suggestive of a tumour - e.g. X-rays , or increasingly MRI and CAT scans. Diagnosis of tissue type usually relies on:
Biopsy- Good biopsies require proper sampling and proper preservation and handling. Fine Needle Aspirate Biopsy involves smearing the sample on a microscope slide. Core biopsies are taken using a specialist needle such as a Tru-Cut. Punch and trephine biopsies are taken with appropriate instruments which cut out a disc of tissue - punch for e.g. skin, and trephine for bone. Full surgical biopsies may involve attempted removal of the mass or taking a section. All these types of sample are preserved in 10% Formalin or Formalin / saline.
With cell/ fluid collection type biopsies such as Cerebrospinal Fluid, then it is customary to make a smear and to preserve some as well to maximise the possibility of a diagnosis. It may be necessary to contact the lab first.
Treatment "Cutting, Burning, Poisoning"
Surgery is still very useful for benign tumours or tumours which are of known extent. De-bulking surgery is also used to prolong life, often alongside other therapies..
Chemotherapy involves using powerful drugs which disrupt cell division. These have side effects because they also affect normal tissues. They are often used in combination to reduce the effects seen with one drug alone.
Radiation therapy is used to damage a tumour's DNA. A tightly focused beam is used to minimise damage to other tissues.
Cryotherapy involves freezing the tissue several times using liquid nitrogen. This kills off the cells, so is only used for tumours which are isolated and accessible..
Complications of neoplasia
1) Physical. Tumours may be so large as to interfere with normal function of the organ, e.g. bowel.
2) Haemorrhage. Some tumours bleed persistently and so cause anaemia. Anaemia may also arise in tumours of the bone marrow.
3) Hypercalcaemia. A few tumour types can cause massive increases in serum calcium levels, e.g. lymphomas, lung masses. This can cause all sorts of problems as calcium is deposited in the kidney, and the nervous system starts to malfunction electrically.
4) Histamine release. A relatively common type of tumour - the mast cell tumour- can release the chemical histamine, causing shock like syndromes, and long-term, gastric ulcers.
5) Pain. Cancer patients may need long term pain relief. This should not be neglected.