Types of dog tumors
Dog cancer can be classified by the various types of cells that are involved in its formation and growth. It is not uncommon for a tumor to have both epithelial and mesenchymal components and not fit cleanly into either category. For example, a tumor of the kidney or the ovaries may contain both mesenchymal and epithelial cells. It can also be difficult to distinguish between benign and malignant tumors, especially if it is an advanced tumor that has already spread.
Epithelial cells are typically epithelial cells lining the surface of the body or lining organs. If they spread outside of these places, then it is called metastasis. Epithelial cells line the inner lining of the mouth, the mucous membranes, the intestines, the lungs, the gallbladder, and the bladder.
Carcinoma or cancer is the term used to describe a malignant epithelial cell growth. Carcinoma may be the single most common form of cancer in dogs and cats and is characterized by growth of abnormal cells. It can also spread to other areas of the body, called metastasis.
A very advanced cancer will have spread beyond the original area, and this is called a disseminated cancer. Disseminated cancers can form tumours (masses of tissue that form when cancer cells spread through the body) and cysts (fluid-filled sacs formed when cancer cells spread through the body and close off normal tissues). When they are found in a dog or cat, it is often too late.
One type of carcinoma is the solid (non-cystic) type. These grow in tissue and may be relatively slow growing. They are commonly referred to as adenocarcinomas. They include solid tumours of the skin, the tongue, the respiratory tract, the intestine, the prostate gland and other organs.
The most common type of carcinoma is the cystic (or cystic-solid) type. These often grow very fast and they may occur in locations where there is a high concentration of hormones. They can be found in the salivary glands of the mouth, the prostate gland of the male and the female reproductive organs (ovaries and uteruses). The cystic carcinomas of the mammary glands are called adenomas (which means ‘tumours’) and are very common. Adenomas are benign, and they may become cystic (developing a cystic solid growth within it) as the tumour grows, but they rarely cause life-threatening problems.
The most common site for bladder cancer is at the base of the urethra. It can sometimes be seen through the rectum. Lymphoma, which also may involve the rectum, is the most common form of lymphoma in dogs and cats.
A metastasis (or metastasising) cancer is cancer that has spread from one or more sites to another. There is a list of metastases in appendix 7.6.1. Metastatic tumours may occur at any site, but in most cases, they occur in tissues that connect with the blood vessels (called vascular), or in lymph nodes and other sites where lymphocytes are found (see also appendix 8.7).
An ameloblastoma is a type of epithelial tumour that grows in the hard tissues of the body and is classified as a benign tumour. It starts to develop in the jaw of dogs and cats. It grows slowly and can become quite large and cause a lot of damage to the mouth. This type of tumour occurs in the jaw (incisor teeth and cheek) of most dogs and cats.
An adenoma is a type of benign tumour, which is a localised, slow-growing, non-invasive neoplasm that tends to arise in epithelial tissues, such as the thyroid, pancreas and colon. Adenomas are common, particularly in dogs and cats. The most common site in dogs is the colon and rectum, and in cats it is the small intestine and the stomach. It is possible for an adenoma to grow into the walls of the small intestine (mucosal or submucosal). Most adenomas can be cured by surgery.
A choristoma is a relatively benign neoplasm that develops in some areas of the body and can take the form of one of a variety of types of tissue. Examples of this type of tumour are hamartoma (benign tumour) and teratoma (tumour formed from the body-building processes of many different tissues).
**Choristomas are relatively rare, occurring in:**
• The skin
• The eye
• The testes
• The salivary glands
• The uterus
• The thyroid glands
• The ovaries
• The brain
• The spinal cord
**cy** -stes (ky-STEHS), noun
* _the plural of cyst_
A cyst is a sac-like cavity that occurs in the body. They are usually enclosed in a membrane, and can be lined by a single layer of cells, a variety of cell layers, or are often a combination of these two.
Cavities can be found throughout the body, although cysts occur particularly in the following locations:
• The kidneys and testes are sites where a number of cysts occur.
• The brain, skull, spinal cord, and the pancreas are the sites where cysts occur more often.
• In humans, the lungs and liver are sites where cysts occur.
• The ovaries and fallopian tubes can develop cysts, too.
• In the digestive system, there are numerous cysts that occur in the stomach, intestines, gallbladder, and liver.
• In the respiratory system, there are cysts that occur in the sinuses, the nose, and the larynx.
• In the ear, the middle ear, outer ear, and the mastoid air cell system contain fluid-filled structures called _mastoids_.
#### ectodermal dysplasia
ek**-te**- **der** -mal dys- **play** -sha, (ad- **play** -shee) _noun_
A congenital disorder in which there is faulty or missing development in the outer layer of the body, which covers the inner organs.
Also spelled as _ectodermal dysplasia_.
• The absence of tooth enamel, which makes teeth have an unusual and unpleasant appearance.
• Failure of the facial skin to develop a complete skin covering.
• The loss of two or more bones in the skull.
#### echis carinatus
ek**-is** car **in** -a- **kut** -us, (e- **chees** ka-rin **ak** -you-tuss) _noun_
A pit viper.
**echis carinatus** _noun_
The species of pit viper found in the Middle East.
**echis carinatus** _noun_
A species of pit viper, which is found in Australia and New Guinea.
**echis carinatus** _noun_
A species of pit viper, which is found in Africa.