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Cancer in Pets – An Overview

Dog resting on the floor.
When cells or tissues in the body begin to grow abnormally and uncontrollably, this is called neoplasia. A tumor, or a swelling of the part of the body, is a created as a result of uncontrolled cell growth. Tumors can be either benign or malignant. A benign tumor is not invasive, meaning the rapidly growing cells are localized to one area and do not invade the rest of the body. However, malignant tumors are made up of cells that spread throughout the body (metastasize) and harm other tissues, most commonly the lung and lymph nodes. The term “cancer” specifically refers to malignant tumors which spread and grow rapidly throughout other areas of the body. Cancer is not one disease, but hundreds. Cancer can be grouped into three main categories: Carcinomas – carcinomas are formed by epithelial cells, which are the cells that cover the inside and outside surfaces of the body. Tumors of the anal gland, mammary gland, and bladder are types of carcinomas in dogs and cats. Hematopoetic tumors – blood cancer, or hematopoetic tumors, include mast cell tumors, leukemia and lymphoma. At the Schwarzman Animal Medical Center, lymphoma is a common cancer treated in both dogs and cats. Lymphoma in Dogs Lymphoma in Cats Sarcomas – sarcomas are tumors formed by cells from bone and soft tissues, including muscle, fat, blood vessels, lymph vessels, and fibrous tissue (such as tendons and ligaments). Examples of sarcomas in dogs include soft tissue sarcoma, hemangiosarcoma, and osteosarcoma.  

Osteosarcoma

An x-ray of osteosarcoma in a dog
Cancer is not one disease, but hundreds. Cancer can be grouped into three main categories: Carcinomas – carcinomas are formed by epithelial cells, which are the cells that cover the inside and outside surfaces of the body. Tumors of the anal gland and mammary gland are common carcinomas in dogs and cats. Hematopoetic tumors – blood cancer, or hematopoetic tumors, include leukemia and lymphoma. Sarcomas – sarcomas are tumors formed by cells from bone and soft tissues, including muscle, fat, blood vessels, lymph vessels, and fibrous tissue (such as tendons and ligaments). Examples of sarcomas in dogs include soft tissue sarcoma, hemangiosarcoma, and osteosarcoma. Osteosarcoma is the most common bone tumor in dogs, accounting for 85% of all canine skeletal tumors. While osteosarcoma is also the most common bone tumor in cats, primary bone tumors are relatively uncommon in cats to begin with. Osteosarcoma is also far less aggressive in cats than it is in dogs. Osteosarcoma typically develops on the limbs (the forelimbs more often than the hindlimbs), but can also occur on the skull, rib cage, and spine. A rare form of osteosarcoma occurs outside the skeleton in the muscles, liver, or spleen. Osteosarcoma is a particularly aggressive tumor in dogs, with 75-90% of patients eventually having the tumor cells metastasize (spread) to other areas, particularly the lungs and other bones. In cats with osteosarcoma, around 40% will metastasize.

Pyometra

Pyometra is a serious bacterial infection of the uterus that occurs most often in older, intact (unspayed) female dogs and cats. The most common bacterium identified in pyometra is E. coli, which typically originates in the feces and ascends through the vagina into the uterus. The infection tends to occur about a month after the dog or cat has been in heat. If unrecognized and untreated, pyometra can lead to a systemic infection or blood poisoning. Pyometra is often described as being “open” or “closed.” With “open” pyometra, the cervix (the part of the uterus that connects with the vagina) is open, allowing the fluid that forms in the uterus due to the infection to drain out of the body through the vagina. With “closed” pyometra, where the cervix is closed, the fluid in the uterus cannot drain through the vagina. Instead, it builds up, stretching the uterine walls and potentially causing the the uterus to rupture. If this occurs, the infection may spread throughout the abdomen leading to shock and, potentially, death. X-ray showing pyometra in a dog X-ray showing pyometra in a cat

Chronic Kidney Disease (CKD)

cat drinking water
Kidney disease refers to the inability of the kidneys to work properly. Kidneys perform several key functions in the body, the most important of which is filtering waste products from the blood. Kidneys also maintain the balance of electrolyte levels in the body (such as sodium, potassium, and chloride), maintain blood pressure, and produce urine. Damage to the kidneys can result in the buildup of waste products to dangerous levels in the blood, also known as azotemia. There are two main types of kidney disease – acute kidney injury (AKI) and chronic kidney disease (CKD). CKD develops slowly over time and can damage the kidneys to the point where they are unable to function properly. CKD was previously termed chronic renal failure (CRF). Unlike acute kidney injury, CKD does not disappear with treatment. CKD affects up to 10% of elderly dogs, while all cats are at risk of developing the disease. Unfortunately, it can take months or even years before a pet with CKD show signs of the disease. In addition, pets that have been diagnosed with AKI are at risk of developing permanent damage to their kidneys which can lead to CKD.  

Acute Kidney Injury (AKI)

Kidney disease refers to the inability of the kidneys to work properly. Kidneys perform several key functions in the body, the most important of which is filtering waste products from the blood. Kidneys also maintain the balance of electrolyte levels in the body (such as sodium, potassium, and chloride), maintain blood pressure, and produce urine. Damage to the kidneys can result in the buildup of waste products to dangerous levels in the blood, also known as azotemia. There are two main types of kidney disease – acute kidney injury (AKI) and chronic kidney disease (CKD). Acute kidney injury was formerly called acute renal failure (ARF) and refers to sudden damage to the kidneys causing a dysfunction. AKI often lasts only for a short period of time and can even disappear completely once the underlying cause is treated. However, pets that have been diagnosed with AKI are at risk of developing permanent damage to their kidneys which can lead to CKD.