LIVER TUMORS AND CANCERS
After blood testing and medical imaging has led us to a diagnosis of liver tumor for a pet, many questions emerge and must be answered in order to make proper choices.
Many of these questions are answered by ultrasound, the most common medium for evaluating the texture of the liver. Unlike radiography, where all soft tissue appears as the same texture, ultrasound is able to separate out tissues depending on their water content. This means that it is possible to see inside the liver and see if there is one tumor or many and how much normal liver texture is left. Ultrasound can determine what organs show tumor inside, whether or not local lymph nodes are enlarged (which could indicate spread of the tumor), and whether or not surgery would be useful. It is also possible to take either a needle aspirate or actual biopsy to determine the type of tumor and knowing the type of tumor will answer remaining questions regarding treatment options, survival time, etc.
Ultrasound video of a liver. The liver is on the left of the screen
WHAT IS THE DIFFERENCE BETWEEN A NEEDLE ASPIRATE AND A BIOPSY?
A biopsy yields a very different sample: an actual chunk of tissue. In this type of sample, the microscopic structures of the liver can be viewed as can the cells infiltrating them. The architecture of the tissue is preserved. Tumors can be graded for the degree of malignancy plus the specific type of tumor is revealed. The downside stems from the fact that a larger piece of tissue is required. Clotting tests must be run prior to the procedure to insure the liver will not bleed. A different type of needle is used and some sort of sedation is typically needed which may add risk. Results typically take longer for a biopsy sample as the laboratory preparation is more complicated. Expense is generally greater for biopsy than for aspirate.
The ultrasonographer typically is in a good position to determine the best balance of risk, expense, and potential information yield.
A correct diagnosis is obtained in 60% of needle aspirates of the liver.
If cancer is found in the liver but is believed not to have originated there, this indicates cancer spread and very advanced disease. Prognosis is poor though what options remain depend on the type of cancer present. Metastatic disease in the liver is approximately two and a half times more common than primary cancer in the liver with most tumors having spread from the spleen, pancreas, or intestinal tract. If your pet appears to be in this situation and you want to obtain all the options possible for palliation of the disease, it is best to consult with an oncology specialist.
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CLASSIFYING PRIMARY TUMORS OF THE LIVER
Again, a primary liver tumor is a tumor that arose in the liver (rather than having spread there from a primary tumor elsewhere). Primary tumors are classified by their shape/configuration within the liver and by the type of liver tissue they originated from. Tumors may be Massive, Nodular, or Diffuse. The best type to have is the “massive” type as this type is present in one area and is thus the most amenable to surgical removal. A “diffuse” tumor involves the entire liver evenly while a “nodular” tumor forms discreet bumps within the liver. While ultrasound can tell us if a tumor is “massive,” “nodular,” or “diffuse.” It cannot tell us the tissue of origin.
The four tissues of origin for primary liver tumors are: Hepatocellular, Bile Duct, Neuroendocrine (also called “carcinoid”), and Mesenchymal.
There are three types of hepatocelluar tumors to be had by dogs and cats, hepatocellular carcinoma (the most common hepatocellular tumor of dogs), hepatocellular adenoma (the most common hepatocellular tumor of cats), and the hepatoblastoma (which is exceedingly rare and has only only been reported in one dog).
The hepatocellular adenoma is benign and does not cause illness. It might cause some blood changes which might, in turn, trigger a medical work up but if a biopsy turns up this tumor in an otherwise healthy pet, the news is good and nothing bad should be expected to come of this tumor. Alternatively, if this diagnosis is made in a pet that it sick, the illness probably cannot be blamed on this tumor and a further search for the right diagnosis is warranted.
The hepatocellular carcinoma is an important tumor of dogs and cats, not only because it is moderately common but because it tends to be amenable to surgery even though it is malignant. In humans, this tumor often has a viral basis (i.e. one of the hepatitis viruses) as well as an association with cirrhosis (scarring in the liver) but in dogs and cats neither of these associations holds true.
Most hepatocellular carcinomas (50-80%) are “massive,”
In dogs, over 2/3 of “massive” cases involve only the left side of the liver.
In dogs, the rate of metastasis is 90-100% for
If the patient, dog or cat, has a massive tumor surgery can greatly improve life quality even if the entire tumor cannot be removed. The hepatocellular carcinoma grows very slowly so surgery, while challenging, typically produces excellent results. The risks of surgery include bleeding, circulatory compromise to the remaining liver portions, reduced liver function after surgery, and transient low blood sugar. The time of greatest risk and concern is the time of the surgery and during surgical recovery. After recovery, one study found a median survival time of 1460 days. If the tumor is present on the right side of the liver, surgery is more difficult as the vena cava, the largest vein in the body, is very close by and may bleed. The bottom line is that massive disease should be addressed with surgery with potential for cure while nodular or diffuse disease has a poor prognosis.
BILE DUCT TUMORS
There are two types of bile duct tumors to be had by dogs and cats: biliary adenoma (benign) and biliary carcinoma (malignant.) The biliary adenoma is the most common primary liver tumor in the cat and accounts for over 50% of all feline primary liver tumors. They are cystic in structure meaning they tend to be large and fluid-filled. They do not cause problems until they are so big that they press on other organs but because they are fluid-filled, the fluid can be periodically sucked out with ultrasound guidance to restore health or the tumor can be removed surgically once and for all.
The biliary carcinoma can be massive, nodular, or diffuse. If the tumor is massive, surgery is generally recommended though this tumor is so malignant that survival times after surgery are typically only about 6 months. Metastasis ultimately occurs in just under 80% of cats and just over 80% in dogs.
These tumors are rare and usually diffuse (2/3 of cases are diffuse and 1/3 are nodular). They tend to spread quickly and early in their course. Prognosis is poor and because they are rare tumors few studies are available to suggest treatment.
The word “mesenchyma” (mezz-en-KY-ma) does not exactly roll off one’s tongue. The mesenchyma of the liver is the general liver tissue separate from the bile ducts etc. inside the liver. Tumors of the mesenchyma are called “sarcomas.”
Primary sarcomas of the liver are unusual but include: hemangiosarcoma (a malignancy of blood vessels which is a common secondary tumor but only 5% of hemangiosarcomas arise in the liver), fibrosarcoma (malignancy of fibrous tissue), osteosarcoma (bone malignancy), and leiomyosarcoma (smooth muscle malignancy). Approximately 36% of sarcomas are massive and 64% are nodular with metastasis found in 80-100% of cases depending on the study. Massive tumors of other types are generally amenable to surgery but in the case of sarcomas, there is usually tumor spread already present. Some tumors can be treated with chemotherapy.
ONE LAST TUMOR
The myelolipoma of the cat is worth mentioning as it carries and excellent prognosis with surgery. This is a benign and often very large tumor consisting of fat mixed with blood cell precursors. Current theory is that it develops in response to poor oxygenation in a particular liver area. Once removed, it should not grow back.
Hopefully, this summary has been helpful in reviewing the possible tumors and what to expect based on how they appear on ultrasound. For specific treatment options, it may be necessary to consult with a specialist. Your regular veterinarian is in the best position to refer you.
Page posted: 7/3/09