Oncology Index

What are connective tissue and nerve tumors?
All tissues and organs of the body may develop cancer (an abnormal overgrowth of their constituent cells). Every organ (liver, lungs, spleen, kidneys and so on) contains a supporting framework of fibrous connective tissue as well as nerves to relay information to and from the brain. Most organs also contain muscle tissue and special cells (histiocytes or macrophages) whose function is to clear debris. Cancers of these tissues can therefore occur anywhere in the body.

Histiocyte biology
Langerhans cells were first recognized under the microscope in 1868 by a medical student, Paul Langerhans. These cells are members of the histiocyte group, which are part of the body’s immune surveillance system. They take up and process foreign antigens, such as pollens and viral, bacterial and fungal microorganisms.

What is this lump?
Cysts are hollow spaces containing liquid or solidified secretion. A few cysts form within cancers but only non-cancerous cysts are considered here.

What is cytology?
Cytology is the microscopic examination of cell samples.

Cancers of the pancreas are of two main types, those arising from the part which produces enzymes to aid digestion (exocrine) and those arising from the groups of cells that produce hormones such as insulin (endocrine). Both groups of tumors may be benign (pancreatic adenomas) or malignant (pancreatic carcinomas).

Muscle (called "smooth muscle") and fibrous connective tissues form the framework (stroma) that holds other tissues together in the organs of the body. They enable these organs to contract and stretch as part of their function, for example in digestion of food. A number of different tumors can develop from the cells of these tissues.

A "tumor" is a lump. Not all are cancerous. Panniculitis is usually visible as a lump but it is an inflammation of the subcutaneous fatty tissue and is not cancerous. Steatitis is a similar inflammation of fatty tissue but occurs in any part of the body.

A "tumor" is a lump. Most, but not all, are cancerous. A large number of different types of tumor, with a bewildering array of names, but often of confusingly similar appearance, can occur in association with the tissues around the eye.

Papillomas are benign, but sometimes multiple, tumors caused by viruses. They are commonly known as "warts". The tumors often disappear spontaneously because the animal slowly develops immunity to them, but some papillomas may need to be removed surgically because they are inflamed, bleeding or infected. They are permanently cured by total surgical removal and do not spread to other parts of the body although there may be multiple tumors.

Parathyroid tumors in dogs include non-cancerous cysts, formed before birth. Enlarged parathyroid glands due to cell overgrowth (hyperplasia) may be secondary to chronic kidney disease and unbalanced nutrition. Most parathyroid cancers are benign (adenomas) and slow growing. Some are malignant (spreading). Both benign and malignant parathyroid cancers produce hormones. The hormones produce signs of overactive parathyroids (" hyperparathyroidism") with clinical signs such as weakening of bones with fractures and lameness. Sometimes there is also loosening and loss of teeth.

Fibrous tissue consists of long fibres of the protein, collagen. These fibers form part of specialized tissues such as bone and cartilage but most are in loose or linear arrangements within low cellularity ground substance. This "connective tissue" is present throughout the body connecting and supporting organs and systems. The basic cell responsible for fiber production is a fibroblast. Overactivity in local areas can produce fibrous tissue masses, mostly slow-growing, non-cancerous and with several names. A few are considered to be benign cancers so are called "fibromas".

This tumor is a disordered and purposeless overgrowth of modified sebaceous glands known as the hepatoid glands. These glands only occur in dogs. They are found in the skin around the anus, prepuce and dorsal tail and occasionally other areas of the skin. The tumor cells resemble liver (hepatic) cells. Most tumors are benign and can be permanently cured by total surgical removal. Many are multiple. Malignant hepatoid gland tumors tend to be locally invasive but very rarely spread to other parts of the body.

Tumors of the intestinal epithelial lining include non-cancerous polyps, benign adenomas and malignant epithelial tumors (adenocarcinomas). The polyps and adenomas may be multiple and cause local obstruction. The malignant tumors cause progressive illness and often spread (metastasize) before clinical diagnosis. Secondary tumors are found in the lymph nodes (glands), on the inside lining of the abdomen (peritoneum) and in the liver and lungs. Survival time with malignant intestinal tumors is often only months, although it is longer if the tumor has not spread before surgery.

Multiple tumors in the liver are not always cancers. The livers of older dogs become nodular although this does not have any clinical effects. Multiple nodules (regenerative nodules) with an accompanying increase in fibrous tissue may be the result of previous liver damage including inflammation of the liver (hepatitis). When the fibrosis affects the whole liver, it is called cirrhosis. At this stage, it is progressive and not curable.

The liver has a massive blood supply so many cancer cells from elsewhere arrive within it and start to grow. In dogs metastatic tumors are three times as common as primary tumors and over 30% of malignant cancer is said to metastasize to the liver. Cancer of the lymph cells of the immune system (lymphosarcoma or lymphoma) is the most common type followed by tumors of the blood vessels (haemangiosarcoma) and then tumors of epithelial tissue, particularly from the pancreas. The liver has multiple functions and a variety of different cells within it so primary cancers may arise from the neuroendocrine cells (carcinoids) and tumors of histiocytic, fibrous and muscle tissue also occur. These are discussed in more detail elsewhere.

What is a tumor of the lymphatics?
This is a tumor of the lymphatic vessels of the skin or subcutaneous tissue.

A malignant mammary tumor is a tumor originating from the mammary gland tissues that has been classified as malignant (invasive and capable of spreading). Although some of these cancers are cured by surgical removal, others recur and some spread to other parts of the body (metastasis). A dog that has a tumor of this type often has or will develop further tumors in other mammary glands.

Mast cells originate in the bone marrow but only mature in peripheral tissues. They are found in all tissues of the body but most are near surfaces in contact with the external environment such as the skin, respiratory and digestive tracts. Mast cells produce many chemicals with differing effects on the body (histamine, proteoglycans, neutral proteases and chemotactic growth factors). These chemicals are present in granules in the cytoplasm of mast cells. They are discharged from the cells in response to various stimuli, and they induce inflammatory reactions. Mast cells also interact with cells of the immune system producing antibodies involved with allergic reactions (immunoglobulin E, IgE), presenting foreign molecules (antigens) and recruiting cells (phagocytes) to engulf foreign material. As well as being a cellular barrier to external agents, they have a regulatory function on nerves, blood circulation, fibrous tissue and other immune cells.

Melanocytes are cells that produce a pigment called melanin. They are found in many parts of the body where there is pigment, particularly skin, hair and eyes.

Melanocytes are cells that produce a pigment called melanin. They are found in many parts of the body where there is pigment, particularly the skin, hair and eyes. In embryonic development, melanocytes are related to cells of the nervous system. Melanogenesis (formation of melanin) is a complex process with genetic, hormonal and ultraviolet (UV) control. A suntan is the result of stimulation of these cells by sunlight (UVA and UVB). Inside the eye melanocytes are found in the iris and choroid layers (see diagram).

What types of nasal tumors are there?
In some cases, chronic inflammation of the nose (rhinitis) leads to proliferation (hyperplasia) and formation of polyps in the nose or throat. These are not cancerous but may need removal. The chronic inflammation is often due to infections with viruses, bacteria and/or fungi and also occurs in animals with a tendency to allergies (atopic animals). Some chronic infections predispose to cancer.

What are neuroendocrine cells?
Neuroendocrine cells interact with the nervous system and produce specialized chemical substances called "neuroendocrine hormones". These hormones affect the rates of specific chemical reactions in other cells locally or in other tissues of the body. Together with the nervous system and other types of hormones they integrate and co-ordinate a wide variety of activities to maintain internal stability of the body. The neuroendocrine hormone producing cells are present in glands such as the adrenal medulla, chemoreceptors (aortic and carotid bodies) and pancreatic islets. They are also scattered throughout the body in a variety of organs including the skin, mouth, esophagus, intestine, liver and lung.

What are neuroendocrine cells and chemoreceptors?
Neuroendocrine cells produce specialized chemical substances called "neuroendocrine hormones". Neuroendocrine hormones interact with the nervous system and other hormones to integrate and co-ordinate a wide variety of activities to maintain internal stability of the body.

What are oral tumors?
An epulis (plural epuli) is the clinical name for a swelling on the gums. Several different tumors share this name, often of different origins including the tooth-socket lining and lining epithelium of the mouth. Most epuli are not cancerous but overgrowths (hyperplasias) as a reaction to trauma. These are fibrous (’fibrous hyperplasia’ or ’fibromatous epulis’). If they are more active, often with bone formation, they are called ’peripheral odontogenic fibroma’ (POF) or ’fibromatous and ossifying epulis’). These originate from the tooth forming tissue. A few of this type are cancerous but benign. Occasionally, these become more malignant and invade locally. Rarely, there is spread to lymph nodes (glands) as fibrosarcomas.

What are fibrosarcomas?
Oral fibrosarcomas are rapidly growing, malignant tumors originating from the fibrous connective tissue of the mouth. The tumors are rarely cured by surgical removal. Recurrence in the mouth and spread to other parts of the body (metastasis) are common.