Hemangiosarcoma is a mesenchymal neoplasm originating in the endothelial cells of blood vessels; they can be classified as non-visceral and visceral types. Non-visceral hemangiosarcomas can affect the skin, subcutaneous tissues, and muscle tissues; visceral hemangiosarcomas can affect the spleen, liver, heart, lungs, kidneys, oral cavity, bones, bladder, uterus, tongue, and retroperitoneum. Among domestic species, dogs are most affected by cutaneous HSA. Cutaneous HSA represents approximately 14% of all HSA diagnosed in this species and less than 5% of dermal tumors, according to North American studies. However, Brazilian epidemiological data demonstrate a higher prevalence, which may represent 27 to 80% of all canine HSAs and 13.9% of all skin neoplasms diagnosed in this species. Cutaneous HSA most commonly affects middle-aged to elderly dogs (between 8 and 15 years old), with no gender predisposition for either the actinic or non-actinic forms. The higher prevalence of cutaneous HSA in some canine breeds is related to lower protection from solar radiation, as low skin pigmentation and hair coverage lead to greater sun exposure. Actinic changes, such as solar dermatosis, are frequent in these patients, confirming the influence of solar radiation on the development of this neoplasm. There are multiple clinical manifestations of hemangiosarcoma in canines. The diagnostic approach and staging classification of cutaneous HSAs are similar between the different subtypes. The definitive diagnosis is obtained through histopathological analysis of incisional or excisional biopsies. Cytology can be used as a presurgical screening test; however, it has little diagnostic utility in cases of HSA because there is a high risk of blood contamination and sample hemodilution. Surgery is generally the treatment of choice for dogs with localized non-visceral HSA without evidence of metastatic disease. Recently, electrochemotherapy (ECT) has emerged as an alternative therapy for the local ablative treatment of different neoplastic types; the use of radiotherapy for the treatment of dogs with cutaneous HSA is uncommon. There is greater consensus in the literature regarding the indications for adjuvant chemotherapy in subcutaneous and muscular HSA; doxorubicin is the most frequently used antineoplastic agent for subcutaneous and muscular subtypes and can be administered alone or in combination with other drugs. Other therapies include antiangiogenic therapy, photodynamic therapy, the association of chemotherapy with the metronomic dose, targeted therapies, and natural products. The benefits of these therapies are presented and discussed. In general, the prognosis of splenic and cardiac HSA is unfavorable. As a challenging neoplasm, studies of new protocols and treatment modalities are necessary to control this aggressive disease.

There are 3 types of leiomyosarcoma of the skin: dermal, subcutaneous, and metastatic cutaneous. Dermal leiomyosarcoma arises from smooth muscle fibers in arrector pili muscles, genital dartos muscles, and the nipple-areola complex. It is an intermediate-grade tumor associated with a tendency for local recurrence (24%) and low metastatic potential (4%). Subcutaneous leiomyosarcoma originates from smooth muscle in blood vessel walls and has higher rates of local recurrence (37%) and metastasis (43%). Plemorphic dermal sarcoma typically affects elderly patients and arises in sun-exposed areas (e.g., the scalp). Its histologic and immunohistochemical characteristics are similar to those of atypical fibroxanthoma, but it is more aggressive (metastasis rate of 10-20%). Histologically, it can be distinguished from atypical fibroxanthoma by the observation of subcutaneous tissue invasion, perineural invasion, and foci of necrosis.

Kaposi sarcoma is a vascular sarcoma with 4 clinical variants: classic Kaposi sarcoma, which mainly affect the extremities of elderly patients and follows a chronic, generally indolent course; African Kaposi sarcoma; immunosuppression-associated Kaposi sarcoma; and AIDS-associated Kaposi sarcoma. Type8 human herpesvirus is the etiologic agent in all 4variants. Cutaneous angiosarcoma is a cutaneous neoplasm with a very poor prognosis. It carries a high probability of local relapse and has a 10% to 15% survival rate at 5years. There are 3 main variants of cutaneous angiosarcoma: idiopathic angiosarcoma of the face and scalp; Stewart-Treves syndrome; and postradiation angiosarcoma. The only potentially curative treatment is surgery with or without radiotherapy. However, its indistinct borders and multicentric nature mean that treatment is often palliative with chemotherapy, radiotherapy, or both.

Kaposi\'s sarcoma is a multifocal vascular lesion of low-grade potential that is most often present in mucocutaneous sites and usually also affects lymph nodes and visceral organs. The condition may manifest through purplish lesions, flat or raised with an irregular shape, gastrointestinal bleeding due to lesions located in the digestive system, and dyspnea and hemoptysis associated with pulmonary lesions. In the early 1980s, the appearance of several cases of Kaposi\'s sarcoma in homosexual men was the first alarm about a newly identified epidemic, acquired immunodeficiency syndrome. In 1994, it was finally demonstrated that the presence of a herpes virus associated with Kaposi\'s sarcoma called HHV-8 or Kaposi\'s sarcoma herpes virus and its genetic sequence was rapidly deciphered. The prevalence of this virus is very high (about 50%) in some African populations, but stands between 2% and 8% for the entire world population. Kaposi\'s sarcoma only develops when the immune system is depressed, as in acquired immunodeficiency syndrome, which appears to be associated with a specific variant of the Kaposi\'s sarcoma herpes virus. There are no treatment guidelines for Kaposi\'s sarcoma established in Brazil, and thus the Brazilian Society of Clinical Oncology and the Brazilian Society of Infectious Diseases developed the treatment consensus presented here.