Hemangiosarcoma is quite common in dogs, and more so in certain breeds including German Shepherd Dogs and Golden Retrievers. It also occurs in cats, but much more rarely. Dogs with hemangiosarcoma rarely show clinical signs until the tumor has become very large and has metastasized. Typically, clinical signs are due to hypovolemia after the tumor ruptures, causing extensive bleeding. Owners of the affected dogs often discover that the dog has hemangiosarcoma only after the dog collapses.

The tumor most often appears on the spleen, right heart base, or liver, although varieties also appear on or under the skin or in other locations. It is the most common tumor of the heart, and occurs in the right atrium or right auricular appendage. Here it can cause right-sided heart failure, arrhythmias, pericardial effusion, and cardiac tamponade. Hemangiosarcoma of the spleen or liver is the most common tumor to cause hemorrhage in the abdomen. Hemorrhage secondary to splenic and hepatic tumors can also cause ventricular arrythmias. Hemangiosarcoma of the skin usually appears as a small red or bluish-black lump. It can also occur under the skin. It is suspected that in the skin, hemangiosarcoma is caused by sun exposure. Occasionally, hemangiosarcoma of the skin can be a metastasis from visceral hemangiosarcoma. Other sites the tumor may occur include bone, kidneys, the bladder, muscle, the mouth, and the central nervous system.

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.

In their early stages, soft-tissue sarcomas usually do not cause symptoms. Because soft tissue is relatively elastic, tumors can grow rather large, pushing aside normal tissue, before they are felt or cause any problems. The first noticeable symptom is usually a painless lump or swelling. As the tumor grows, it may cause other symptoms, such as pain or soreness, as it presses against nearby nerves and muscles. If in the abdomen it can cause abdominal pains commonly mistaken for menstrual cramps, indigestion, or cause constipation.

Hemangioendothelioma is used to describe a group of vascular neoplasms that may be considered benign as well as malignant, depending on the specific group member's activity.

A soft-tissue sarcoma is a form of sarcoma that develops in connective tissue, though the term is sometimes applied to elements of the soft tissue that are not currently considered connective tissue.

The sarcoma first appears as a bruise mark, a purplish discoloration or a tender skin nodule in the extremity, typically on the anterior surface. It progresses to an ulcer with crusting, and finally to an extensive necrosis involving the skin and subcutaneous tissue. It metastasizes quickly.

Hemangioendotheliomas may be classified as:

- "Epithelioid sarcoma-like hemangioendothelioma" is an exceedingly rare vascular tumor of intermediate grade that was first described by Steven Billings, Andrew Folpe, and Sharon Weiss in 2003. These tumors are so named because their histologic appearance is very similar to that of epithelioid sarcoma, a more malignant tumor with which they are commonly mistaken.

- "Composite hemangioendothelioma" is a low-grade angiosarcoma typically occurring in adults, although it has been described in infancy.

- "Spindle-cell hemangioendothelioma") is a vascular tumor that was first described in 1986 by Sharon Weiss, M.D., and commonly presents in a child or young adult who develops blue nodules of firm consistency on a distal extremity. These tumors were reclassified by Dr. Weiss in 1996 as "spindle cell hemangioma", rather than hemangioendothelioma, due to the excellent prognosis observed in a group of 78 patients.

- "Retiform hemangioendothelioma" (also known as a "Hobnail hemangioendothelioma") is a low-grade angiosarcoma, first described in 1994, presenting as a slow-growing exophytic mass, dermal plaque, or subcutaneous nodule.

- "Kaposiform hemangioendothelioma" (also known as "Infantile kaposiform hemangioendothelioma") is an uncommon vascular tumor, first described by Niedt, Greco, et al. (Hemangioma with Kaposi's sarcoma-like features: report of two cases.(Niedt GW, Greco MA, Wieczorek R, Blanc WA, Knowles DM 2nd. that affects infants and young children, with rare cases having also been reported in adults.Pediatr Pathol. 1989;9(5):567-75.)

- "Endovascular papillary angioendothelioma", also known as "Dabska tumor", "papillary intralymphatic angioendothelioma" (PILA), "Dabska-type hemangioendothelioma", "hobnail hemangioendothelioma", and "malignant endovascular papillary angioendothelioma", is a rare low-grade angiosarcoma of lymphatic channels. Approximately 30 such tumors have been described in the medical literature. Although included in the World Health Organization tumor classification, there is uncertainty as to whether EPA is a distinct entity or a heterogenous group of tumours. The lesion usually presents as a slow-growing tumor of the skin and subcutaneous tissues of the head, neck, or extremity, of infants or young children. However, EPA has involved the testicle, deep muscle tissue as a neoplastic transformation of a larger existing benign cavernous hemangioma, bone and spleen, and has been found in adults. Some reports indicate a good prognosis but metastasis is occasionally seen.

- "Infantile hemangioendothelioma" is a rare benign vascular tumour arising from mesenchymal tissue and is usually located in the liver. It often presents in infancy with cardiac failure because of extensive arteriovenous shunting within the lesion. It is the third most common liver tumor in children, the most common benign vascular tumor of the liver in infancy, and the most common symptomatic liver tumor during the first 6 months of life. These hemangioendotheliomas have 2 growth phases: an initial rapid growth phase, which is followed by a period of spontaneous involution (usually within the first 12 to 18 months of life). Detection of the hemangioendothelioma within the first 6 months of life is attributed to the initial rapid growth during this time; however, the tumor has been detected with fetal ultrasonography. Histopathologically, there are 2 types of hepatic hemangioendotheliomas:

- Type I: Hemagioendotheliomas of this type have multiple vascular channels that are formed by an immature endothelial lining with stromal separation from bile ductules.

- Type II: These hemangioendotheliomas have an appearance that is more disorganized and hypercellular, and there are no bile ductules.

Lymphangiosarcoma is a rare malignant tumor which occurs in long-standing cases of primary or secondary lymphedema. It involves either the upper or lower lymphedematous extremities but is most common in upper extremities. Although its name implies lymphatic origin, it is believed to arise from endothelial cells and may be more accurately referred to as angiosarcoma.

Heart cancer is an extremely rare form of cancer that is divided into primary tumors of the heart and secondary tumors of the heart.

Angiosarcoma is a cancer of the cells that line the walls of blood vessels or lymphatic vessels. The lining of the vessel walls is called the endothelium. Cancers from the walls of blood vessels are called hemangiosarcomas, and cancers from the walls of lymphatic vessels are called lymphangiosarcomas. However, they should not be confused with cherry hemangiomas.

Most tumors of visceral blood and lymphatic vessel walls are cancerous (malignant). Because these cancers are carried by the blood flow or lymphatic flow, they can more easily metastasize to distant sites, particularly the liver and lungs.

Angiosarcomas will show signs of hemorrhage and necrosis. Pathologically, tumor cells will show increased nuclear to cytoplasm ratio, nuclear hyperchromasia, nuclear pleomorphism and high mitotic activity.

In dogs, hemangiosarcoma is relatively common, especially in larger breeds such as golden retrievers and Labrador retrievers. In humans, hemangiosarcomas and lymphangiosarcomas of the skin are uncommon. Angiosarcoma of the liver, a rare fatal tumor, has been seen in workers intensively exposed to the gas vinyl chloride monomer (VCM) for prolonged periods while working in polyvinyl chloride (PVC) polymerization plants. It has also been associated with individuals exposed to arsenic-containing insecticides and Thorotrast.

Intravascular papillary endothelial hyperplasia (also known as "Masson's hemangio-endotheliome vegetant intravasculaire," "Masson's lesion," "Masson's pseudoangiosarcoma," "Masson's tumor," and "Papillary endothelial hyperplasia") is a rare, benign tumor. It may mimic an angiosarcoma, with lesions that are red or purplish 5-mm to 5-cm papules and deep nodules on the head, neck, or upper extremities.

Most heart tumors begin with myxomas, fibromas, rhabdomyomas, and hamartomas, although malignant sarcomas (such as angiosarcoma or cardiac sarcoma) have been known to occur. In a study of 12,487 autopsies performed in Hong Kong seven cardiac tumors were found, most of which were benign. According to Mayo Clinic: "At Mayo Clinic, on average only one case of heart cancer is seen each year." In a study conducted in the Hospital of the Medical University of Vienna 113 primary cardiac tumour cases were identified in a time period of 15 years with 11 being malignant. The mean survival in the latter group of patients was found to be .

Primary malignant cardiac tumors (PMCTs) are even more rare. A study using the Surveillance, Epidemiology and End-Results (SEER) Cancer Registry from 1973–2011 found 551 cases of PMCTs, with an incidence of 34 cases per million persons. The study also found that the incidence has doubled over the past four decades. The associated mortality was very high, with only 46% of patients alive after one year. Sarcomas and mesotheliomas had the worst survival, while lymphomas had better survival. When compared with extracardiac tumors, PMCTs had worse survival.

Lewis lung carcinoma is a tumor discovered by Dr. Margaret R. Lewis of the Wistar Institute in 1951. This tumor originated spontaneously as a carcinoma of the lung of a C57BL mouse. The tumor does not appear to be grossly hemorrhagic and the majority of the tumor tissue is a semifirm homogeneous mass. It is also called 3LL and LLC and is used as a transplantable malignancy. It has been used in many studies.

In 1975, Munson discovered that cannabinoids suppress Lewis lung carcinoma cell growth. The mechanism of this action was shown to be inhibition of DNA synthesis Cannabinoids increase the life span of mice carrying Lewis lung tumors and decrease primary tumor size. There are multiple modes of action.

A mammary tumor is a neoplasm originating in the mammary gland. It is a common finding in older female dogs and cats that are not spayed, but they are found in other animals as well. The mammary glands in dogs and cats are associated with their nipples and extend from the underside of the chest to the groin on both sides of the midline. There are many differences between mammary tumors in animals and breast cancer in humans, including tumor type, malignancy, and treatment options. The prevalence in dogs is about three times that of women. In dogs, mammary tumors are the second most common tumor (after skin tumors) over all and the most common tumor in female dogs with a reported incidence of 3.4%. Multiple studies have documented that spaying female dogs when young greatly decreases their risk of developing mammary neoplasia when aged. Compared with female dogs left intact, those spayed before puberty have 0.5% of the risk, those spayed after one estrous cycle have 8.0% of the risk, and dogs spayed after two estrous cycles have 26.0% of the risk of developing mammary neoplasia later in life. Overall, unspayed female dogs have a seven times greater risk of developing mammary neoplasia than do those that are spayed. While the benefit of spaying decreases with each estrous cycle, some benefit has been demonstrated in female dogs even up to 9 years of age. There is a much lower risk (about 1 percent) in male dogs and a risk in cats about half that of dogs.

The exact causes for the development of canine mammary tumors are not fully understood. However, hormones of the estrous cycle seem to be involved. Female dogs who are not spayed or who are spayed later than the first heat cycle are more likely to develop mammary tumors. Dogs have an overall reported incidence of mammary tumors of 3.4 percent. Dogs spayed before their first heat have 0.5 percent of this risk, and dogs spayed after just one heat cycle have 8 percent of this risk. The tumors are often multiple. The average age of dogs with mammary tumors is ten to eleven years old. Obesity at one year of age and eating red meat have also been associated with an increased risk for these tumors, as has the feeding of high fat homemade diets.

There are several hypotheses on the molecular mechanisms involved in the development of canine mammary tumors but a specific genetic mutation has not been identified.

In breast pathology, pseudoangiomatous stromal hyperplasia, commonly abbreviated PASH, is an overgrowth of myofibroblastic cells and has an appearance similar to fibroadenomatoid changes.

The diagnostic significance is currently uncertain, but it appears to be benign. There have been cases of PASH diagnosed where the tumors co-exist with breast cancer. Other cases have made screening for breast cancer difficult and in some cases impossible due to the number and density of the existing PASH tumors. These cases have resulted in the necessity of a mastectomy and double mastectomy.

The diagnosis of PASH is by biopsy.

The important differential diagnosis is angiosarcoma, from which it was first differentiated in 1986.

Stewart–Treves syndrome, also known as cutaneous angiosarcoma, refers to a lymphangiosarcoma, a rare complication that forms as a result of chronic, long-standing lymphedema. Although it most commonly refers to malignancies associated with chronic lymphedema resulting from mastectomy and/or radiotherapy for breast cancer, it may also describe lymphangiosarcomas that result from congenital and other causes of chronic secondary lymphedema. Lymphangiosarcoma arising from cancer-related lymphedema has become much less common with better surgical techniques, radiation therapy, and conservative treatment. The prognosis, even with wide surgical excision and subsequent radiotherapy, is poor.

Early detection is key. Untreated patients usually live 5 to 8 months after diagnosis.

The term multiple endocrine neoplasia (MEN) encompasses several distinct syndromes featuring tumors of endocrine glands, each with its own characteristic pattern. In some cases, the tumors are malignant, in others, benign. Benign or malignant tumors of nonendocrine tissues occur as components of some of these tumor syndromes.

MEN syndromes are inherited as autosomal dominant disorders.

Primary pigmented nodular adrenocortical disease (PPNAD) was first coined in 1984 by Carney et al. it often occurs in association with Carney complex (CNC). CNC is a rare syndrome that involves the formation of abnormal tumours that cause endocrine hyperactivity.

PPNAD arises due to the enlargement of the cortex of the adrenal glands, resulting in Cushing's syndrome that is independent of the pituitary hormone ACTH.

PPNAD is a rare cause of high cortisol levels in the blood and often manifests as ACTH-independent Cushing's syndrome. The effects of PPNAD can often be cyclical so the symptoms of Cushing's syndrome will not always be as severe, which may complicate diagnosis. The classic symptoms of Cushing's syndrome include rapid central weight gain, a puffy red face and a buffalo hump at the back of the neck due to fat deposits. Skin changes in Cushing's syndrome include thinning and bruising easily, developing striae and hyperpigmentation at skin folds. The hormonal changes can lead to hirsuitism, males developing breast tissue, females no longer having periods and both sexes may become infertile. High cortisol levels can lead to psychological disturbances such as anxiety or depression and insomnia. Bone health can deteriorate, leading to an increased fracture risk in people with Cushing's syndrome. PPNAD is unique as it often causes Cushing's at a young age, in children and adolescents. In addition to the other symptoms of Cushing's syndrome, the patient may have a short stature due to interrupted growth because of ACTH suppression.

In 90% of people with PPNAD it is associated with Carney Complex. Carney Complex is usually inherited, however it can also occur sporadically. A visible sign of Carney complex is abnormal skin hyperpigmentation. There may also be myxomas which can appear as lumps in the skin and breast as well as often being present in the heart, which can lead to multiple cardiovascular problems. The majority of people with PPNAD will have some of these signs/symptoms due to the strong association between PPNAD and Carney Complex.

The older names, "multiple endocrine adenomas" and "multiple endocrine adenomatosis" (MEA), have been replaced by the current terminology.

The term multiple endocrine neoplasia is used when two or more endocrine tumor types, known to occur as a part of one of the defined MEN syndromes, occurs in a single patient and there is evidence for either a causative mutation or hereditary transmission. The presence of two or more tumor types in a single patient does not automatically designate that individual as having MEN because there is a small statistical chance that development of two "sporadic" tumors that occur in one of the MEN syndromes could occur by chance.

The term "multiple endocrine neoplasia" was introduced in 1968, but descriptions of the condition date back to 1903.

Pleural tumors may be benign (i.e. solitary fibromas) or malignant in nature. Pleural Mesothelioma is a type of malignant cancer associated with asbestos exposure.

- Mesothelial tumors: pleural malignant mesothelioma.

- Pleural sarcomas

- Pleural angiosarcoma

- Pleural desmoplastic small round cell tumor (pleural DSRCT)

- Pleural synovial sarcoma

- Pleural solitary fibrous tumor (pleural SFT)

- Smooth muscle tumors of the pleura

- Pleural carcinomas

- Pleural mucoepidermoid carcinoma

- Pleural pseudomesotheliomatous adenocarcinoma

Costello syndrome, also called faciocutaneoskeletal syndrome or FCS syndrome, is a rare genetic disorder that affects many parts of the body. It is characterized by delayed development and delayed mental progression, distinctive facial features, unusually flexible joints, and loose folds of extra skin, especially on the hands and feet. Heart abnormalities are common, including a very fast heartbeat (tachycardia), structural heart defects, and overgrowth of the heart muscle (hypertrophic cardiomyopathy). Infants with Costello syndrome may be large at birth, but grow more slowly than other children and have difficulty feeding. Later in life, people with this condition have relatively short stature and many have reduced levels of growth hormones. It is a RASopathy.

Beginning in early childhood, people with Costello syndrome have an increased risk of developing certain cancerous and noncancerous tumors. Small growths called papillomas are the most common noncancerous tumors seen with this condition. They usually develop around the nose and mouth or near the anus. The most frequent cancerous tumor associated with Costello syndrome is a soft tissue tumor called a rhabdomyosarcoma. Other cancers also have been reported in children and adolescents with this disorder, including a tumor that arises in developing nerve cells (neuroblastoma) and a form of bladder cancer (transitional cell carcinoma).

Costello Syndrome was discovered by Dr Jack Costello, a New Zealand Paediatrician in 1977. He is credited with first reporting the syndrome in the Australian Paediatric Journal, Volume 13, No.2 in 1977.