Primary tumours of the liver and biliary system are genuinely rare in cats, accounting for only about 1.0 to 2.9 percent of all feline neoplasms. They can arise from hepatocytes, the biliary epithelium, neuroendocrine cells or connective tissue elements, producing a histologically diverse group of diseases with very different behaviours. Because these tumours are uncommon, most published evidence has consisted of small single-institution case series, which has made it difficult for clinicians to give owners accurate prognostic information. The new study, led by Carolyn Averil Hylton and Matteo Rossanese of the Royal Veterinary College with colleagues at Colorado State University, the University of Bologna and the San Marco Veterinary Clinic, set out to close that evidence gap by pooling cases treated between 2003 and 2024.

The cohort was dominated by domestic shorthairs, reflecting the general cat population, with a median age of 12 years and a median body weight of 4.8 kilograms. Only eight of the 76 cats were asymptomatic; in these animals a mass was discovered incidentally during investigations for unrelated problems. The rest presented with the vague, non-specific signs typical of feline hepatic disease: lethargy, reduced appetite, progressive weight loss, vomiting and abdominal distension. Advanced cases could show icterus, clotting abnormalities and excessive thirst and urination, all signs of failing liver function. The median duration of clinical signs before presentation was 29 days, a reminder of how quietly these tumours can grow in a species that hides illness well.

Diagnostic workups revealed the scale of the problem. Imaging identified hepatic masses with a median maximal diameter of 5.5 centimetres, with the largest reaching 13 centimetres, an extraordinary volume for a feline liver. The left division of the liver was involved in 40 of the 76 cases, the central division in 22 and the right division in 14. The overwhelming majority of tumours, 85.5 percent, were of the massive solitary type rather than nodular or diffuse. Biliary cystadenoma, a benign tumour of the bile duct epithelium, was the most common diagnosis with 30 cases, followed by hepatocellular carcinoma with 19, hepatocellular adenoma with 11 and biliary carcinoma with 11, alongside small numbers of haemangiosarcomas and neuroendocrine carcinomas.

Preoperative diagnosis proved as difficult as the literature suggests. Nearly two-thirds of the masses were sampled before surgery, mostly by fine needle aspiration, but cytology matched the final histopathology in only 22 of those samples, was inconclusive in 11 and flatly wrong in 9, and in two further cases the pathologists could not distinguish adenoma from carcinoma. All seven tru-cut biopsy samples, by contrast, proved accurate. The study also uncovered biochemical patterns that may help clinicians refine their suspicion. Cats with biliary carcinoma had markedly elevated total bilirubin concentrations, with a median of 191 micromoles per litre, likely reflecting mechanical obstruction of bile flow, whereas cats with biliary cystadenoma had a median bilirubin of just 3 micromoles per litre. Cats with the benign cystadenomas also had significantly lower ALT and ALP liver enzyme values than cats with malignant tumours, consistent with the greater hepatocyte injury caused by carcinomas.

All 76 cats underwent exploratory abdominal surgery performed by or under the direct supervision of board-certified veterinary surgeons, with complete liver lobectomy in 66 cases and partial lobectomy in 10. A third of the cats required resection of more than one liver lobe, an operationally significant finding that underscores how large and invasive these masses can be. The authors suggest the predominance of left-sided tumours may partly reflect surgical selection bias: left lateral masses sit away from the gallbladder, bile ducts and hepatic hilus and are easier to resect, so surgeons and owners may historically have opted for surgery mainly in that anatomically favourable setting. Still, a genuine biological predilection for the larger left hepatic parenchyma cannot be excluded.

The headline safety data are striking. Intraoperative complications occurred in 11 cats, about 15 percent, including four severe haemorrhagic events. Postoperatively, 17 cats, 22 percent, experienced complications ranging from hyperthermia and anaemia requiring transfusion to anorexia severe enough to need a feeding tube. Seven cats died as a result of perioperative complications, giving an overall mortality rate of just 9 percent, with 69 of 76 cats surviving to hospital discharge. The median hospitalisation was four days. Earlier reports had put survival to discharge as low as 40 percent, so the authors argue that improvements in diagnostics, anaesthesia and surgical technique over recent decades have fundamentally changed the risk calculus for this operation.

Survival analysis, using Kaplan–Meier curves and Cox proportional hazards modelling, showed that histological diagnosis was the only factor significantly associated with survival. Median tumour-specific survival for cats with malignant tumours was 673 days, compared with 2916 days for benign tumours, a difference that was highly statistically significant. Among the malignant subtypes, cats with hepatocellular carcinoma lived a median of 859 days and those with biliary carcinoma 387 days, while for biliary cystadenoma the median survival was never reached during follow-up, which extended to nearly eight years in some patients. Notably, incomplete surgical margins did not significantly affect survival, nor did tumour size or location, although the authors caution that the mix of benign and malignant lesions among incompletely excised tumours may have muddied that comparison.

Recurrence and metastasis rates appeared reassuringly low, at 18 and 25 percent respectively among the cats for which restaging data were available, occurring between 30 and 840 days and 30 and 435 days after surgery. However, the authors flag an important limitation: only 28 of the 69 surviving cats underwent any follow-up restaging, so the true recurrence figures remain uncertain. Only four cats received postoperative chemotherapy, too few to draw any conclusion about the value of adjunctive therapy. The retrospective design also introduces selection bias, since cats deemed inoperable, those with metastatic disease at diagnosis and those euthanised without surgery were necessarily excluded, likely inflating the reported survival times.

Even with those caveats, the study delivers a clear and clinically actionable message. Liver lobectomy for feline hepatobiliary tumours carries a low mortality rate, and even cats with hepatocellular or biliary carcinoma can achieve favourable survival measured in years rather than weeks, outcomes consistent with recent smaller studies and broadly comparable to results in dogs. The authors recommend that clinicians actively discuss surgical options with owners of cats presenting with hepatic masses rather than defaulting to palliative management on the basis of outdated expectations. They also propose that surgery should be considered for masses outside the anatomically convenient left division, and that marked bilirubin elevations may warrant heightened suspicion of biliary carcinoma when cytology is inconclusive. Larger prospective studies will be needed to identify reliable prognostic factors and define the role of chemotherapy, but for now, the message to feline practitioners is one of cautious optimism: for many cats with primary liver tumours, surgery works, and it works better than the old textbooks ever admitted.

Subject of Research: Survival and prognostic factors in cats undergoing surgery for primary non-lymphomatous hepatobiliary tumours

Article Title: Evaluation of survival and prognostic factors in cats undergoing surgery for primary non-lymphomatous hepatobiliary tumours

Article References: Hylton, C. A., Guillén, A., Altwal, J., Tremolada, G., Cinti, F., Magno, S. D., & Rossanese, M. (2026). Evaluation of survival and prognostic factors in cats undergoing surgery for primary non-lymphomatous hepatobiliary tumours. Veterinary Oncology, 3(1), Article 2. https://doi.org/10.1186/s44356-025-00053-0

Image Credits: AI Generated

DOI: 10.1186/s44356-025-00053-0

Keywords: feline, hepatobiliary tumours, liver lobectomy, veterinary oncology, hepatocellular carcinoma, biliary cystadenoma, biliary carcinoma, prognostic factors, tumour-specific survival, surgical complications, retrospective study, liver enzymes