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Tumors by Location

A tumor is an abnormal mass of tissue that results when cells divide more rapidly than normal, or do not die when they should, and can develop from any normal tissue type; therefore there are a considerable number of different tumor locations. Tumors may also be referred to as a neoplasm. Cancer refers to the disease of uncontrolled cell growth which can be benign (not invasive and does not spread) or malignant (invasive into surrounding tissue and capable of spreading to other areas of the body).

For each tissue type listed below, specific terminology is used to denote the origin of the tumor and whether the tumor is benign or malignant. Below are also common tumor types listed by location or tissue type. For more information about specific tumor cell lines please see the Tumors by Name section of this website.

To better understand cancer terminology, visit the Cancer Dictionary at the website of the National Cancer Institute (NCI) and the National Institute of Health (NIH).

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Definitions

Adrenal

Adrenal gland tumors are rare and vary considerably in terms of type, secondary signs, treatment, and outcome.
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Almost any sign may be associated with adrenal tumors. Two general types of adrenal tumors exist: adrenocortical carcinoma and pheochromocytoma. A variety of blood tests and imaging studies may be needed to confirm a diagnosis. Treatment is generally with surgery, although some cases may respond to medical management (chemotherapy). Surgery can be difficult due to frequent invasion of large blood vessels (vena cava) and the kidney. Secondary changes due to hormone production from the tumor may complicate treatment.
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Anal Sac

Anal sac tumors occur most commonly in female dogs and are usually malignant (apocrine gland adenocarcinoma).
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Some tumors result in increased blood calcium levels. Signs may vary from a lump in the anal sac or enlarged lymph nodes causing changes in stools or straining, to signs secondary to increased calcium (hypercalcemia): increased water consumption, increased urination, weight loss, and vomiting. Many of these tumors have already spread to lymph nodes in the abdomen before the diagnosis can be made. Treatment includes surgical removal of the anal sac and possibly lymph nodes. In some cases radiation therapy and chemotherapy is also recommended. Medical treatment of increased calcium may be needed before or after tumor treatment to decrease injury to the kidneys.
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Anus

Tumors of the anus (not the anal sac) are most common in male dogs.
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Benign tumors (perianal adenomas) are hormone dependent and occur most commonly in dogs that have not been castrated. Malignant tumors (sebaceous gland adenocarcinomas) are not hormone dependent. Benign tumors are treated with local tumor removal (surgery/cryosurgery) and castration (to prevent new tumor development). Treatment and outcome of malignant tumors vary depending on tumor size and possible spread to lymph nodes but generally include surgery and possibly radiation therapy.
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Bladder

Bladder cancer is more common in dogs than cats.
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Most tumors are malignant (transitional cell carcinoma) and can spread to lymph nodes, bone, and lung. Signs include blood in the urine, straining to urinate, or signs secondary to tumor spread. Surgery often is not an option due to the location of these tumors in the bladder, although chemotherapy with or without radiation therapy may be viable treatment options. Cures are difficult due to inability to totally remove the bladder tumor and the high chance of tumor spread beyond the bladder.
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Bone

Bone cancer is more common in dogs than cats.
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Most cases are malignant (usually osteosarcoma), but a wide variation in clinical signs, location, and outcome after treatment exists. When possible, the affected bone is removed surgically (including leg amputation), although radiation therapy is sometimes used to treat the affected bone. Depending on the degree of malignancy, chemotherapy is often indicated after surgery.
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Brain

Brain tumors are more common in dogs than cats.
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A wide variety of tumors and clinical signs may be seen depending on the site and size of the tumor, and include blindness, seizures, and changes in personality. Diagnosis usually requires a CT or MRI scan. Treatment varies depending on location and size but may involve surgery and/or radiation therapy. Cats with meningioma (a specific brain tumor) have the best outcomes with appropriate treatment.
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Esophagus

These rare tumors result in vomiting, regurgitation, or weight loss.
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Treatment is difficult unless the tumor is benign and surgically removable.
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Eye (Ocular)

Ocular tumors only affect a small percentage of dogs and cats but because of their location even benign tumors may cause blindness and loss of the eye.
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The most common tumors of the eyelids, third eyelids and ocular surface are papillomas, adenomas, and melanomas in dogs and squamous cell carcinomas in cats. These tumors are most commonly treated by surgical removal or cryosurgery. The most common primary ocular tumors in dogs and cats are melanomas. In this case, enucleation is the most common form of treatment, where the eye is removed, if there are concerns for malignancy. This form of treatment is curative. Malignant melanomas that are metastatic carry a poorer prognosis.
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Kidney

Kidney cancer is rare in dogs and cats and may start in the kidney itself, spread to the kidney from another whole-body cancer, or be part of another cancer called lymphoma.
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Signs are varied but include back pain, blood in the urine, weight loss, fever, and abdominal enlargement. Treatment is usually with surgery if the remaining kidney is functioning well. Lymphoma is treated with chemotherapy. Response to treatment varies considerably from good to poor.
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Large Intestine (see Rectum)
Liver

Liver cancer is not common in dogs or cats.
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It can start in the liver, or spread to the liver from another cancer in the body. Clinical signs are often vague and include weight loss, loss of appetite, fatigue, abdominal enlargement, and possible jaundice. Solitary tumors (even if very large) may be effectively treated with surgery.
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Lung

Lung cancer is less common in animals compared to humans and affects dogs more frequently than cats.
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It can start in the lung or spread to the lung (metastasis) from another cancer somewhere else in the body. Treatment for a tumor that originates in the lung usually involves surgical removal of the affected lung. If the disease is spread from another location, surgery is generally not a good option.
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Lymphatic Tissue

Lymphoma is a disease that often arises from lymphatic tissue, and disease may involve lymph nodes, liver, spleen, and bone marrow.
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This disease is more common in this presentation in dogs, while more common in the gastrointestinal tract of cats. This is a treatable, not curable disease. Treatment includes chemotherapy.

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Mammary (Breast)

Cancer in the mammary glands is very common in dogs and cats. It is often hormone dependent for its initial development.
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Dogs and cats that are spayed early in life (less than one year of age) have almost no risk of developing malignant breast cancer. Approximately 50% of dog breast tumors are malignant while 90% of cat tumors are. Treatment is with surgery (mastectomy). The role of chemotherapy and radiation are undefined at this time. Over half of dogs are cured by surgery, whereas cat tumors are more malignant.
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Muscle

Cancer that originates from muscle is rare in dogs and cats. Leiomyomas and leiomyosarcomas are tumors arising from smooth muscle.
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Leimyomas are benign. Leiomyosarcomas are malignant tumors and are the second most common gastrointestinal tumor of dogs. In most cases, surgery is the treatment of choice. Rhabdomyosarcoma is a tumor that arises from striated muscle. In dogs these tumors most often arise from the tongue, larynx, myocardium, and bladder. These tumors require a multi modal treatment regimen and typically have a fair to poor prognosis.
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Nerves

Cancer of nerves that originate in the brain or spinal cord is uncommon.
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It may occur close to the brain or spinal cord, which causes the symptoms, or can occur in nerves away from the brain or spinal cord (see soft tissue sarcomas, peripheral nerve sheath tumors). Treatment is with surgery or occasionally radiation.
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Oral

Cancer of the oral cavity is common in dogs and less common in cats.
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A very wide range of tumors can occur from very malignant to benign. Signs may include difficulty eating, swelling inside or outside the mouth, halitosis (bad breath), and bloody saliva. A biopsy is critical for accurate diagnosis and treatment planning. Treatment is generally with surgery (possibly including bone removing procedures) and/or radiation. The outcome of treatment is extremely variable depending on tumor type, site, size, and species.
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Ovary

Cancer of the ovary is uncommon in dogs and cats.
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Clinical signs vary and include a distended abdomen from the tumor or fluid production. Some ovarian cancers produce excess hormones resulting in prolonged or absent heat cycles and hair loss. Treatment is surgical removal of the ovaries and outcomes are good if the tumor has not spread to other sites within the abdomen.
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Pituitary

Pituitary tumors occur in a specialized part of the bottom of the brain.
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They may or may not result in increased stimulation of various hormones (especially cortisone from the adrenal glands). Signs (increased water consumption, hair loss, etc.) may be from overproduction of hormones or related to pressure on the brain causing blindness, seizures, or change in personality. Treatment may involve medical management of symptoms or radiation of the tumor itself.
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Prostate

This cancer is rare in animals (compared to humans) and is much more common in dogs than cats.
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Most cases are in the advanced stages of disease when first diagnosed. Treatment is often ineffective compared to treatment in humans. Treatment options include radiation therapy, chemotherapy, and therapy with a non-steroidal anti-inflammatory.
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Rectum

Cancer of the colon or rectum (large intestine) is rare.
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Common signs can include blood in the bowel movement or straining to have a bowel movement. Tumors may be benign (polyps) or malignant. Treatment is generally with surgical removal or occasionally with cryosurgery (polyps). Prognosis varies depending on tumor type, specific site, and completeness of surgical removal.
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Skin

Skin tumors are the most common tumors in dogs and cats.
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Over half of skin tumors are benign (especially in dogs), but all skin lumps deserve attention for the possibility of malignancy. Taking a few cells out of these tumors (fine-needle aspiration cytology) can help determine benign from malignant tumors. Management may include observation (only if it is conclusively benign), surgery, cryosurgery or, rarely, radiation or chemotherapy. Outcome ranges dramatically based on tumor type, site, size, species, and degree of malignancy.
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Small Intestine

Small intestinal tumors are rare and can result in vomiting, diarrhea, or weight loss.
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Treatment is usually with surgery, although chemotherapy may be used to treat intestinal lymphoma.
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Spinal Cord

Spinal cord tumors are rare.
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They may start in the spinal cord or the spinal cord may be affected by a tumor starting in tissue adjacent to the spinal cord (e.g., bone, nerve, or muscle). Signs are usually associated with pain, lameness or paralysis, and vary with which site in the spinal cord is affected. Treatment varies widely and includes surgery, radiation and, rarely, chemotherapy. Outcome also varies widely depending on tumor type, site, and degree of spinal cord injury prior to treatment.
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Spleen

Cancer of the spleen is more common in dogs than cats.
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Many non-cancerous conditions can cause enlargement of the spleen or lumps on the spleen. When the spleen does have cancer, it can originate in the spleen or be part of other whole body diseases. Signs of splenic cancer vary from weight loss, fatigue, enlargement of the abdomen and rapid collapse (from bleeding). Treatment is generally with splenectomy (removal of the spleen) and survival varies widely depending on the type of tumor and whether it has spread elsewhere. Chemotherapy is used for treatment (before or after spleen removal) in certain cases.
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Stomach

Stomach cancer is rare in dogs and cats.
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Signs vary but may include vomiting (especially if blood is present), weight loss, anemia, and lack of appetite. Bowel movements may be dark and tarry in nature. Most stomach tumors are malignant with evidence of spread to lymph nodes or liver making treatment difficult. Treatment is generally with surgery, especially for benign tumors, although they are rare.
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Testicles

Cancer of the testicles is common in older dogs and rare in cats.
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Tumors are often benign but malignant forms do occur, especially in undescended testicles. They may produce hormones with secondary signs such as hair loss, feminization, or increased prostate size. Treatment is with castration and the outcome is usually excellent.
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Uterus

Uterine cancer is rare in animals and can be malignant or benign.
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It is more malignant in cats. Signs may include an abdominal mass or vaginal discharge. Some tumors are dependent on hormones for growth and treatment includes removing the ovaries and the uterus (spay).
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Vagina

Tumors of the vagina are more common in dogs that are not spayed.
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Signs include vaginal discharge, a physical mass, and straining to urinate. Growth may increase during heat cycles. Many of these tumors are benign (leiomyoma or polyp) and respond very well to surgical removal and spaying. A rare tumor (transmissible venereal cell tumor) is spread from dog to dog by sexual contact and can be cured with chemotherapy (vincristine) or radiation therapy.
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Vascular (Blood Vessels)

Hemangioma and hemangiosarcoma (HSA) are tumors of vascular endothelial origin (lining of blood vessels).
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Hemangioma is a benign tumor that can occur in a variety of sites, including skin, liver spleen, kidneys, bone, tongue and heart. Complete surgical resection is usually curative. Hemangiosarcomas are highly malignant tumors. The most common primary sites in cats and dogs involve the visceral organs such as the spleen, right atrium of the heart, and liver. Tumors may also be in the skin or below the skin. Treatment is wide surgical resection, and typically chemotherapy as well. Hemangiosarcoma generally carries a poor prognosis.
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