A histiocytoma in the dog is a benign tumor. It is an abnormal growth in the skin of histiocytes (histiocytosis), a cell that is part of the immune system. A similar disease in humans, Hashimoto-Pritzker disease, is also a Langerhans cell histiocytosis. Dog breeds that may be more at risk for this tumor include Bulldogs, American Pit Bull Terriers, American Staffordshire Terriers, Scottish Terriers, Greyhounds, Boxers, and Boston Terriers. They also rarely occur in goats and cattle.

Most histiocytomas will regress within two or three months. Surgical removal may be necessary if the tumor does not regress or if it is growing rapidly to a large size. Histiocytomas should never be treated with an intralesional injection of a corticosteroid, as remission relies on recognition of the tumour by the body's immune system which is suppressed by steroids.

Untreated dogs have an average survival time of 60 days. Lymphoma with a histologic high grade generally respond better to treatment but have shorter survival times than dogs with low grade lymphoma. Dogs with B-lymphocyte tumors have a longer survival time than T-lymphocyte tumors. Mediastinal lymphoma has a poorer prognosis than other types, especially those with hypercalcemia. Clinical stage and substage have some prognostic value, with poorer prognosis associated with Stage V disease, and with substage b (clinical illness at time of presentation).

A histiocytoma is a tumour consisting of histiocytes. Histiocytes are cells that are a part of the mononuclear phagocytic system, a part of the body's immune system that consists of phagocytic cells, which are responsible for engulfing solid particles by the cell membrane to form an internal phagosome by phagocytes and protists.

Types include:

- myxofibrosarcoma

- benign fibrous histiocytoma

- malignant fibrous histiocytoma

- histiocytoma (dog)

Lymphoma is the most common malignancy diagnosed in cats. Lymphoma in young cats occurs most frequently following infection with feline leukemia virus (FeLV) or to a lesser degree feline immunodeficiency virus (FIV). These cats tend to have involvement of lymph nodes, spine, or mediastinum. Cats with FeLV are 62 times more likely to develop lymphoma, and cats with both FeLV and FIV are 77 times more likely. Younger cats tend to have T-cell lymphoma and older cats tend to have B-cell lymphoma. Older cats tend to have gastrointestinal lymphoma without FeLV infection, although tests more sensitive to low level FeLV infections and replication-defective FeLV have found that many of these cats have been previously exposed. The same forms of lymphoma that are found in dogs also occur in cats, but gastrointestinal is the most common type. Lymphoma of the kidney is the most common kidney tumor in cats, and lymphoma is also the most common heart tumor.

It is characterized cystic blood-filled spaces and composed of histiocyte-like cells. A lymphocytic cuff is common. It often simulates a vascular lesion, and was initially described as doing this.

AFH typically has a chromosomal translocation involving the ATF1 gene -- t(12;16) FUS/ATF1 or t(12;22) EWS/ATF1.

Angiomatoid fibrous histiocytoma, abbreviated AFH, is a rarely metastasizing tumour that affects children and young adults.

Prognosis depends on the primary tumor grade (appearance under the microscope as judged by a pathologist), size, resectability (whether it can be completely removed surgically), and presence of metastases. The five-year survival is 80%.

New vaccine protocols have been put forth by the American Association of Feline Practitioners that limit type and frequency of vaccinations given to cats. Specifically, the vaccine for feline leukemia virus should only be given to kittens and high risk cats. Feline rhinotracheitis/panleukopenia/calicivirus vaccines should be given as kittens, a year later and then every three years. Also, vaccines should be given in areas making removal of VAS easier, namely: as close as possible to the tip of the right rear paw for rabies, the tip of the left rear paw for feline leukemia (unless combined with rabies), and on the right shoulder—being careful to avoid the midline or interscapular space—for other vaccines (such as FVRCP). There have been no specific associations between development of VAS and vaccine brand or manufacturer, concurrent infections, history of trauma, or environment.

Undifferentiated pleomorphic sarcoma is regarded as the most common soft tissue sarcoma of late adult life. It rarely occurs in children. It occurs more often in Caucasians than in those of African or Asian descent and is a male-predominant disease, afflicting two males for every female.

Inflammation in the subcutis following vaccination is considered to be a risk factor in the development of VAS, and vaccines containing aluminum were found to produce more inflammation. Furthermore, particles of aluminum adjuvant have been discovered in tumor macrophages. In addition, individual genetic characteristics can also contribute to these injection-site sarcomas. The incidence of VAS is between 1 in 1,000 to 1 in 10,000 vaccinated cats and has been found to be dose-dependent. The time from vaccination to tumor formation varies from three months to eleven years. Fibrosarcoma is the most common VAS; other types include rhabdomyosarcoma, myxosarcoma, chondrosarcoma, malignant fibrous histiocytoma, and undifferentiated sarcoma.

Similar examples of sarcomas developing secondary to inflammation include tumors associated with metallic implants and foreign body material in humans, and sarcomas of the esophagus associated with "Spirocerca lupi" infection in dogs and ocular sarcomas in cats following trauma. Cats may be the predominant species to develop VAS because they have an increased susceptibility to oxidative injury, as evidenced also by an increased risk of Heinz body anemia and acetaminophen toxicity.

Cancer prevalence in dogs increases with age and certain breeds are more susceptible to specific kinds of cancers. Millions of dogs develop spontaneous tumors each year. Boxers, Boston Terriers and Golden Retrievers are among the breeds that most commonly develop mast cell tumors. Large and giant breeds, like Great Danes, Rottweilers, Greyhound and Saint Bernards, are much more likely to develop bone cancer than smaller breeds. Lymphoma occurs at increased rates in Bernese Mountain dogs, bulldogs, and boxers. It is important for the owner to be familiar with the diseases to which their specific breed of dog might have a breed predisposition.

Many types of skin tumors, both benign (noncancerous) and malignant (cancerous), exist. Approximately 20-40% of primary skin tumors are malignant in dogs and 50-65%

are malignant in cats. Not all forms of skin cancer in cats and dogs are caused by sun exposure, but it can happen occasionally. On dogs, the nose and pads of the feet contain sensitive skin and no fur to protect from the sun. Also, cats and dogs with thin or light-colored coats are at a higher risk of sun damage over their entire bodies.

The Xanthogranulomatous Process (XP), also known as Xanthogranulomatous Inflammation is a form of acute and chronic inflammation characterized by an exuberant clustering of foamy macrophages among other inflammatory cells. Localization in the kidney and renal pelvis has been the most frequent and better known occurrence followed by that in the gallbladder but many others have been subsequently recorded. The pathological findings of the process and etiopathogenetic and clinical observations have been reviewed by Cozzutto and Carbone.

Ectomesenchymoma is a rare, fast-growing tumor of the nervous system or soft tissue that occurs mainly in children, although cases have been reported in patients up to age 60. Ectomesenchymomas may form in the head and neck, abdomen, perineum, scrotum, or limbs. Also called malignant ectomesenchymoma.

Malignant ectomesenchymoma (MEM) is a rare tumor of soft tissues or the CNS, which is composed of both neuroectodermal elements [represented by ganglion cells and/or well-differentiated or poorly differentiated neuroblastic cells such as ganglioneuroma, ganglioneuroblastoma, neuroblastoma, peripheral primitive neuroectodermal tumors – PNET] and one or more mesenchymal neoplastic elements, usually rhabdomyosarcoma . The most accepted theory suggests that this tumor arises from remnants of migratory neural crest cells and thus from the ectomesenchyme.

Depending on the pet's unique condition, there are several treatment options, including surgery, chemotherapy and radiation therapy. Treating the pain adequately is also of crucial importance to improve the pet's quality of life, especially if amputation is not performed.

The tumor largely affects children under 15 years of age and about 20% only are found in adults with nearly 60% involving males and 40% females (1). The most frequent locations are head and neck (orbit and nasopharynx), central nervous system, abdomen and retroperitoneum, pelvis, perineum, scrotum and prostate(1). Clinical symptoms are not specific and usually caused by local tumor compression and infiltration.

In male dogs, the tumor affects the penis and foreskin. In female dogs, it affects the vulva. Rarely, the mouth or nose are affected. The tumor often has a cauliflower-like appearance. Signs of genital TVT include a discharge from the prepuce and in some cases urinary retention, from blockage of the urethra. Signs of a nasal TVT include nasal fistulae, nosebleeds and other nasal discharge, facial swelling, and enlargement of the submandibular lymph nodes.

The most common bone tumor is called osteosarcoma, and typically affects middle-age to older dogs of large and giant breeds. Osteosarcoma is less common in cats. Osteosarcoma is an aggressive cancer that can develop in any bone of the body but the majority is seen in the limbs (e.g. long bones such as radius, humerus, femur, and tibia).

Malignant fibrous cytoma is a soft tissue sarcoma that usually occurs in the limbs, most commonly the legs, and may also occur in the abdomen. Also called malignant fibrous histiocytoma.

Surgery may be difficult due to the location of these tumors. Surgery alone often leads to recurrence. Chemotherapy is very effective for TVTs. The prognosis for complete remission with chemotherapy is excellent. The most common chemotherapy agents used are vincristine, vinblastine, and doxorubicin. Radiotherapy may be required if chemotherapy does not work.

Presenting complaints and clinical signs are usually related to the site of origin of the primary tumor or to the presence of metastases, spontaneous tumor rupture, coagulopathies, or cardiac arrhythmias. More than 50% of patients are presented because of acute collapse after spontaneous rupture of the primary tumor or its metastases. Some episodes of collapse are a result of ventricular arrhythmias, which are relatively common in dogs with splenic or cardiac HSA.

Most common clinical signs of visceral hemangiosarcoma include loss of appetite, arrhythmias, weight loss, weakness, lethargy, collapse, pale mucous membranes, and/or sudden death. An enlarged abdomen is often seen due to hemorrhage. Metastasis is most commonly to the liver, omentum, lungs, or brain.

A retrospective study published in 1999 by Ware, "et al.", found a 5 times greater risk of cardiac hemangiosarcoma in spayed vs. intact female dogs and a 2.4 times greater risk of hemangiosarcoma in neutered dogs as compared to intact males.

Hemangiosarcoma is a rapidly growing, highly invasive variety of cancer that occurs almost exclusively in dogs, and only rarely in cats, horses, mice, or humans. It is a sarcoma arising from the lining of blood vessels; that is, blood-filled channels and spaces are commonly observed microscopically. A frequent cause of death is the rupturing of this tumor, causing the patient to rapidly bleed to death.

The term "angiosarcoma", when used without a modifier, usually refers to hemangiosarcoma. However, glomangiosarcoma (8710/3) and lymphangiosarcoma (9170/3) are distinct conditions [in humans]. Hemangiosarcomas are commonly associated with toxic exposure to thorium dioxide (Thorotrast), vinyl chloride, and arsenic.

Progressive nodular histiocytoma is a cutaneous condition characterized by generalized, discrete yellow papules and nodules with prominent facial involvement.

The specific treatment will depend on the tumor's type, location, size, and whether the cancer has spread to other organs. Surgical removal of the tumor remains the standard treatment of choice, but additional forms of therapy such as radiation therapy, chemotherapy, or immunotherapy exist.

When detected early, skin cancer in cats and dogs can often be treated successfully. In many cases, a biopsy can remove the whole tumor, as long as the healthy tissues removed from just outside the tumor area do not contain any cancer cells.