Global state-of-the-art treatment
3.1 Hepatectomy
The liver surface is convex and it slightly touches the diaphragm. The liver is located on the left side of the caudoventral tract, contacting the stomach, duodenum, pancreas, and right kidney.
There are six hepatic lobes: right medial and lateral, left medial and lateral, and quadrate and caudate lobes. The gallbladder is located between the right medial and quadrate lobes. The liver has two so-called afferent (ingoing) blood supplies: the portal system and the arterial system, while the efferent (outgoing) blood flow of the liver circulation is through the hepatic veins. The hepatic lobules, which are the basic functional units of the liver, are cross-sectioned in a hexagonal shape and the portal triads in the periphery. Portal triads consist of the hepatic artery, portal vein, and bile duct. From the anatomic and histologic views, the liver is complicated, and hepatic tissue is friable. Partial lobectomy is difficult and may injure blood vessels and bile ducts in canine patients with bleeding disorders. Many techniques for partial and complete liver lobe resection have been introduced, and numerous stapling instruments have been adopted for both lobectomies. The survey of Liptak et al. [1], which covered 48 dogs with large massive hepatocellular carcinomas during a decade, revealed that their median survival time exceeded 1,460 days after the hepatectomy procedure. However, numerous complications, including ongoing anemia, hepatopathy, ileus, and lack of appetite, are frequently after liver surgery. Therefore, a proper intensive care is recommended to mitigate these complications and minimize the related risks.3.2 Chemotherapy
The most commonly chemotherapy is administered intravenously. According to clinical chemotherapeutic management of neoplastic cases, a significant advance in veterinary practice is observed.
However, a large share of HCC canine patients cannot be cured by chemotherapy and require a further integration of conventional treatment modalities, such as surgery, radiation therapy, and innovative chemotherapy methods. Chemotherapeutic agents are generally administered at the maximum tolerated dose and at the highest dose intensity that is usually used in combination. Four advantages of combination chemotherapy include an increased log-kill, prevention of cancer drug resistance, targeting both dividing and resting cells, and allowing for lower doses with less toxicity [6]. Chemotherapeutic agents damage activated pathogenic cells but also affect normal tissues that divide rapidly and are sensitive to anti-mitotic drugs, such as cells in the bone marrow, digestive tract, and hair follicles. The most common side-effects of chemotherapy are myelosuppression, mucositis, and alopecia. In general, malignant tumors cannot be wholly removed surgically and imply a poor prognosis for canine patients. Palliative chemotherapy and other treatments may be gradually applied to delay the tumor progression. Any further health care should involve close monitoring and minimization of side effects.3.3 Radiotherapy
As a general rule, surgical resection is considered the best treatment option if a primary tumor can be completely excised. If the region of extensive involvement, normal tissue, or volume of liver tumor make its complete removal problematic, then radiotherapy may be recommended by veterinarians as a palliative treatment of liver tumors. Its effectiveness against the canine liver tumor is limited by the fact that canine patients cannot tolerate cumulative doses exceeding 30 Gy [29]. A share of radiotherapy treatment in US veterinary facilities in 2001 study did not exceed 20% [30], while 92% of facilities in 2010 used the 3D computerized radiotherapy, and 20-100% (with median of 50%) of facilities implemented computer simulation treatment plans [31]. It should be noted the abdominal movement caused by breathing during radiotherapy of liver tumors strongly deteriorates the therapeutic effect, which issue can be resolved for human patients but is hard to control with canine ones.
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