Liver tumours in dogs – symptoms, tests and treatment

Overview

A primary liver tumour starts in the liver's own cells. A secondary liver tumour is a metastasis that has spread from elsewhere in the body. In dogs, metastases occur in the liver more often than tumours originating there.

Primary tumours of the liver, gallbladder and bile ducts account for less than 2% of canine cancers. The most common primary liver tumour in dogs is hepatocellular carcinoma, or HCC, a cancer of liver cells. Bile duct carcinoma is the second most common canine liver tumour.

Not every nodule seen in the liver is cancer: older dogs also develop nodular hyperplasia, a benign overgrowth of tissue. This overgrowth usually causes no symptoms and needs no treatment.

Causes

A tumour develops when control of cell multiplication is disrupted and tissue grows uncontrollably in the liver. The precise cause of primary liver tumours is unknown. As well as liver cells, tumours can arise from bile duct cells, blood vessels, connective tissue or hormone-secreting cells.

The massive form of hepatocellular carcinoma means a large tumour usually affecting one lobe. In the nodular form, separate tumour nodules affect several lobes. In the diffuse form, tumour spreads widely through liver tissue without clearly defined nodules.

Around 61% of hepatocellular carcinomas are the massive form. The nodular form accounts for 29%. The diffuse form accounts for 10%.

Metastases may initially be present within liver blood and lymphatic vessels before visible deposits form in the tissue.

A large hepatocellular adenoma may outgrow its blood supply, leaving dead tissue in its centre. This necrotic area can also become the starting point for an abscess.

Risk factors

Primary liver tumours are identified particularly in dogs over 9 years old. They can occur in any breed. A clear single cause usually cannot be identified in an affected dog's living conditions or care.

Cancer originating elsewhere is a different situation: a pancreatic, intestinal or mammary tumour, for example, may spread to the liver. Lymphoma, a cancer of lymphoid tissue, can also affect the liver locally or as part of more widespread disease.

Benign hepatocellular adenomas and precancerous cell changes are identified more often in dogs with adrenal hyperplasia associated with excessive production of sex hormones such as androgens or progesterone.

Typical symptoms

Signs are often vague and do not themselves reveal that the problem is in the liver region.

• Appetite declines, and a dog that previously ate well leaves meals unfinished.

• Weight falls and your dog gradually looks thinner.

• Your dog is more subdued than usual and cannot manage its normal routine.

• Repeated vomiting may occur.

• Your dog drinks and urinates more than usual.

• The abdomen looks enlarged because of liver enlargement or fluid accumulation.

• The whites of the eyes, gums or skin become yellowish.

• Severe cases involve unsteadiness, confusion, weakness or seizures.

Around 75% of dogs with liver tumours show signs of illness. Sometimes the only early finding is a repeatedly increasing liver enzyme value, even though the dog appears healthy at home.

Complications and consequences

Bleeding, bile duct obstruction and low blood sugar

A tumour can rupture and cause life-threatening bleeding into the abdomen. Even a benign tumour's large size is not harmless if it compresses other structures or starts bleeding. A tumour can press on the common bile duct and prevent normal bile flow into the intestine, causing jaundice.

A tumour may lower blood sugar through high glucose consumption or by releasing insulin-like substances. Low blood sugar has been identified in up to 40% of dogs with liver or biliary tumours.

The outlook depends on tumour type and whether removal is possible

After surgery for a removable hepatocellular carcinoma, survival often exceeds 3.8 years. Metastases are identified in less than 5% of surgically treated hepatocellular carcinoma patients. This figure does not apply to all liver tumours, as the outlook also depends on completeness of removal and disease spread.

In hepatocellular tumours, metastatic risk has also been reported as 20–60%, depending on tumour form. For bile duct tumours, the corresponding proportion is around 80%. For neuroendocrine tumours, or carcinoids, it is around 90%.

Hepatocellular carcinoma left without surgery has been associated with a 15-fold risk of death from tumour complications compared with removed tumours. The outlook for bile duct carcinoma is often weeks or months because the disease invades surrounding tissues and spreads readily. Sarcomas and carcinoids generally have a poor outlook because many have already spread at diagnosis.

Metastatic cancer can also cause neurological signs through deposits in the brain. With hepatic haemangiosarcoma, surgery may stop bleeding, but long-term benefit remains limited for most dogs.

Diagnosis at the vet

Blood tests and imaging answer different questions

The vet reviews the progression of symptoms and previous blood results and feels the abdomen. Examination may identify an enlarged liver, a separate mass, fluid or pain. The blood count is checked for findings such as anaemia, a reduction in red blood cells caused by bleeding.

Alongside liver enzymes, bile acids, ammonia and blood-clotting ability are checked where necessary. An increased liver value does not identify tumour type or even confirm a tumour. Metastases may be present even when liver enzyme values are normal.

Ultrasound detects liver masses more sensitively than radiography and helps determine whether changes affect one or several lobes. It also assesses possible bile duct and gallbladder obstruction. Ultrasound alone cannot determine whether a lesion is benign or malignant.

Computed tomography helps plan surgery and search for metastases in the lungs and abdomen. A very large tumour may make it difficult to distinguish whether it compresses neighbouring structures or invades them.

Hepatic lymphoma may go unrecognised on ultrasound because obvious nodules or structural changes do not always develop. If lymphoma is suspected, enlarged lymph nodes or the spleen may also be sampled.

Sampling confirms the nature of the tissue

Fine-needle sampling collects cells under ultrasound guidance for a pathologist to examine. However, it may give a false-negative result if no tumour cells enter the needle. A larger tissue sample is often needed to confirm tumour type.

A biopsy can be taken with an ultrasound-guided core needle, during laparoscopy or at open surgery. Before sampling, bleeding risk is assessed by testing clotting. As well as providing a diagnosis, histopathology indicates how the tumour is likely to behave.

A hepatic myelolipoma is a benign tumour consisting of fat and blood-cell-forming tissue. It can be identified from the cells seen in a fine-needle sample.

Treatment

A localised tumour may be removed surgically

Your vet selects treatment according to tumour type, size and spread. A massive hepatocellular carcinoma confined to one area can often be removed even if large. The procedure removes the tumour or affected liver lobe.

Liver tissue can regenerate, so removal of a substantial portion may be possible. Nodular and diffuse tumours affecting several lobes are generally unsuitable for removal. Hepatocellular carcinoma in left-sided liver lobes generally has a better outlook than at other sites.

Bleeding is a major surgical risk, and preparations for transfusion are made in advance where necessary. Tumour location may also prevent removal of all abnormal tissue. The edges of removed tissue are marked for the pathologist, who assesses whether tumour cells reach them.

Where necessary, biopsies are also collected from liver tissue farther from the tumour to look for cell changes that affect recurrence risk.

A myelolipoma usually needs no removal unless it compresses major blood vessels or bile ducts.

Postoperative monitoring and other treatment options

After surgery, your dog is monitored and receives pain-relieving medication. Blood tests look for internal bleeding and organ dysfunction during recovery. Ongoing postoperative bleeding occurs in less than 2% of operated patients, but can be fatal.

With inoperable or metastatic disease, medication may aim to slow growth and ease symptoms. The effectiveness of conventional systemic chemotherapy for primary liver tumours is not well established. Lymphoma affecting the liver may be treated with chemotherapy appropriate to that tumour type.

In selected cases, a catheter can deliver an embolic material or chemotherapy into the tumour's blood vessel. This embolisation or chemoembolisation may be considered particularly for a localised tumour that cannot be operated on. Benefit and suitability are assessed individually because the effect on survival remains uncertain.

Prevention

There is no known reliable way to prevent primary liver tumours because their cause has not been identified. Breed does not rule out disease, as liver and biliary tumours occur in older dogs of all breeds. Some tumours can be detected because of blood-test changes before visible symptoms. Investigating repeatedly abnormal liver values helps identify progressive liver disease, even though the value alone does not provide a diagnosis.

Dietary changes and supplements have not been shown to prevent canine cancer, so they cannot be used as reliable liver tumour prevention. A balanced diet is chosen according to the dog's overall health and nutritional needs.

Important for dog owners

Bring previous blood results, imaging reports and any histopathology report. Record weight trends, eating, vomiting, drinking and everyday energy. Ask whether the finding is a primary liver tumour or a metastasis and which tumour type is suspected. Request a clear explanation of whether treatment aims to remove the tumour or relieve symptoms.

After surgery, prevent wound licking with a protective collar or shirt according to veterinary instructions. A postoperative check often takes place 10–14 days after surgery. If precancerous cell changes are found in other liver lobes, ultrasound and blood monitoring may be increased to watch for recurrence.

Frequently asked questions

Is a liver tumour always cancer?

No: liver tumours can be benign or malignant. A nodule in an older dog may also be benign tissue overgrowth. However, even a large benign tumour can press on other organs or rupture and bleed, so the finding is investigated.

Can a dog live for years after liver tumour surgery?

Yes, if it is a removable hepatocellular carcinoma: survival after surgery often exceeds 3.8 years. Carcinoids and sarcomas generally have a poor outlook because spread is often already present at diagnosis. Histopathology, surgical margins and the presence of metastases refine an individual dog's outlook.

Does liver cancer show up on a routine blood test?

A blood test may show anaemia from bleeding, meaning a reduced red blood cell count. Liver enzymes can remain normal with metastases, so normal blood results do not rule out a tumour. Identifying tumour type usually requires imaging and a cell or tissue sample.

Why is a biopsy needed if ultrasound shows a tumour?

Ultrasound shows the location and extent of a lesion, but cannot reliably distinguish benign from malignant changes. A pathologist examines tissue structure and identifies the tumour type. Histopathology also provides information on likely tumour behaviour.

Can a large liver tumour still be operable?

Large size does not automatically prevent surgery if the tumour is confined to a removable liver region. Liver tissue can regenerate from the remaining portion. However, nodular or diffuse hepatocellular carcinoma spread across several lobes is generally unsuitable for removal.