adjacent normal tissue. Preoperative evaluation with CT and MRI imaging can be helpful to discriminate tumor from normal tissue (muscle, etc.) (Kim et al. 2005; McEntee and Thrall 2001). Tumor definition and shape have been reported as the most useful parameters in computer tomography to differentiate between lipomas and infiltrative lipomas (Spoldi et al. 2017).
Complete surgical excision is curative; however, this is complicated by the difficulty in distinguishing tumor tissue from normal fat and their infiltrative nature (most often in muscle), which both can result in incomplete resection and tumor recurrence (Kim et al. 2005). In a study of Bergman et al. (1994), a recurrence rate of 36% was reported after aggressive surgical resection. Dogs with infiltrative lipoma may benefit from external beam irradiation alone or in combination with surgery, or multiple cytoreductive surgeries, resulting in long‐term local tumor control (McEntee et al. 2000). An 11‐year‐old Labrador retriever suffering from pelvic limb paraparesis caused by an infiltrative lipoma resulting in spinal cord compression at the fifth thoracic intervertebral space recovered to full ambulatory after mass removal by hemilaminectomy and survived over 24 months after surgery (Morgan et al. 2007). Also, Hobert et al. (2013) reported two dogs with histologically confirmed infiltrative lipoma causing spinal cord compression. In our experience, surgical liposuction of the mass of the tumor leads to DFIs of approximately one year.
Intermuscular lipoma of the thigh is often misdiagnosed as an infiltrative lipoma. An accurate diagnosis is important such that the appropriate treatment is performed. Intermuscular lipomas are treated by marginal excision whereas infiltrative lipomas of the thigh are sometimes treated by amputation or radiation therapy.
Liposarcoma
Liposarcomas are uncommon neoplasms of dogs and cats. There is no breed or sex predilection. Liposarcomas are locally invasive and can metastasize. They consist of malignant lipoblasts and mesenchymal tissue. Most liposarcomas are cutaneous, but they can also develop in the abdominal cavity (Alvarez et al. 2017; Baez et al. 2004).
Oil red O histochemistry can be performed to confirm the presence of lipid and the diagnosis of liposarcoma in cases that are not well differentiated. LaDouceur et al. (2017) reported an overlap in the expression of several muscle antigens and UCP1 between liposarcoma, hibernoma (benign soft tissue tumors containing prominent brown adipocytes), and rhabdomyosarcoma.
The presence of a heterogeneous mass on CT, with a multinodular soft tissue component and associated regional lymphadenopathy and mineralization, are features favoring a diagnosis of liposarcoma (Spoldi et al. 2017). All liposarcoma enhance with contrast medium administration, contrary to infiltrative lipomas. Other CT features associated with canine liposarcomas include heterogeneous internal attenuation (81%) and lack of a clearly defined capsule (38%) suggesting infiltration of local structures (Fuerst et al. 2017).
Survival time is strongly correlated to the type of surgery that is performed. Median survival times are reported of 1188, 649, and 183 days for dogs that underwent wide excision, marginal excision, and incisional biopsy, respectively. Apart from wide excision, tumor size, tumor location, and histologic subtype are associated with survival time (Baez et al. 2004).
The effect of chemotherapy and radiation therapy on this tumor type has not been evaluated (Baez et al. 2004).
Lymphangiosarcoma
Lymphangiosarcoma is a highly malignant neoplasm of the lymphatic endothelium. Lymphangiosarcomas are rare in dogs and cats. Lymphangiosarcoma in the majority of human and canine patients is an aggressively malignant tumor, with few patients surviving despite various attempted surgical and adjunctive treatments. The tumor has been reported mostly in medium‐ to large‐breed dogs, slightly more frequently in males than females, with an age range of 8 weeks to 13 years, with the majority of being in the age group of 5 years and older. The tumor commonly arises in the subcutaneous tissues, rapidly invades underlying tissues, and can spread via the hematogenous and lymphatic routes to frequently involve the pleura and chest. Lymphoid oozing of the skin is sometimes observed (Galeotti et al. 2004; Jackson et al. 2011; Mineshige et al. 2015; Thongtharb et al. 2015; Williams 2005).
Early tissue biopsies for histology and immunochemistry are recommended for progressive edematous lesions of unknown origin as cytology consisted of mild inflammation in dogs diagnosed with lymphangiosarcoma (Curran et al. 2016).
The cell‐specific immunohistochemical lymphatic vessel endothelial receptor‐1 (LYVE‐1) has been successfully used as a marker to diagnose lymphangiosarcoma in cats (Galeotti et al. 2004). LYVE‐1 in conjunction with Prospero‐related homeobox gene‐1 (PROX‐1) is recommended by Halsey et al. (2016) to differentiate between lymphangiosarcoma and HSA in dogs.
The prognosis is poor, with reported survival times being only a few months (Lenard et al. 2007; Williams 2005) up to over one year. In case series of 12 dogs, survival ranged from 60 to 876 days for 3 dogs with palliation; 90 days with prednisone in 1; 182 days with chemotherapy in 1; 240–941 days for 5 dogs receiving surgery; and 574 days for 1 receiving surgery, radiation, and chemotherapy. One dog is alive with recurrence at 243 days following surgery and carboplatin chemotherapy (Curran et al. 2016).
A five‐year‐old Giant schnauzer, suffering from chylothorax and a lymphangiosarcoma involving the whole left sublumbar area was treated surgically by mass resection, pleural omentalization, and pericardiectomy followed by mitoxantrone administration. The dog was still alive 10 months after surgery (Sicotte et al. 2012).
Doxorubicin treatment resulted in a six‐month recurrence‐free interval in a five‐year‐old female Boxer after incomplete local resection in the area of the caudal mammary gland. At relapse Toceranib resulted in almost complete regression of a lymphangiosarcoma, leaving just a skin plaque. Metronomic chemotherapy using chlorambucil and meloxicam had failed to adequately control the disease in this dog (Marcinowska et al. 2013).
Leiomyoma and Leiomyosarcoma
Cutaneous smooth muscle is present in three separate locations: arrector pili muscles, blood vessel walls, and genital/areolar skin. Benign or malignant smooth muscle neoplasms may arise from each of these locations. In dogs, leiomyomas of arrector pili muscles have been described (Cooper and Valentine 2002; Goldschmidt and Shofer 1998).
Leiomyosarcoma are malignant tumors of smooth muscle cells. They mainly are associated with the digestive tract, but they can occur in any part of the body as firm lobulated masses (Cohen et al. 2003; Kapatkin et al. 1992; Pierini et al. 2017). Leiomyosarcomas of the skin do not tend to metastasize, in contrast to hepatic leiomyosarcomas (100%). The prognosis in dogs with leiomyosarcoma of the spleen, stomach, small intestine, and especially the cecum is good to excellent if surgery is performed. In dogs with leiomyosarcoma of the liver, the prognosis is poor (Kapatkin et al. 1992).
Surgical removal of the lesions is the treatment of choice (Liu and Mikaelian 2003).
Doxorubicin has been used as adjunctive therapy after surgical removal of a primary leiomyosarcoma involving the jugular vein in a dog. The dog received five doses of intravenous doxorubicin, and there was no recurrence of the tumor 30 months post treatment (Pierini et al. 2017).
Melanoma
Benign melanocytic tumors comprise 3–4% of all skin tumors in dogs and 0.6–1.3% in cats. Malignant melanocytic tumors generally termed melanoma or malignant melanoma (MM), account for 0.8–2% of all cutaneous tumors in dogs and 0.4–2.8% in cats (Gross et al. 2005; Vail and Withrow 2007). MMs are more common in dogs with heavily pigmented skin, whereas cats with black or gray hair coats may be predisposed (Gross et al. 2005). Cutaneous and ocular melanomas in dogs
