It can be devastating tell a dog owner that their pet has carcinomatosis and will likely pass away shortly after diagnosis. However, it’s not always an immediate death sentence. There are treatment options you can offer owners, which can help improve their quality of life and prolong their survival during this terrible time. However, it is important for pet owners to be aware that there is no cure.

First, let’s begin with some information about carcinomatosis in dogs.

Carcinomatosis refers to widespread dissemination of malignant epithelial cancer, with metastasis to the visceral and/or parietal pleura.

Carcinomatosis is rare in dogs, and can occur anywhere. The most common sites are the abdominal and/or chest cavity. Carcinomatosis may present with or without malignant effusions.

Older dogs are most commonly affected by both mesothelioma and carcinomatosis. However, carcinomatosis can occur in young dogs. There is no breed or gender predilection.

The most common presenting sign is dyspnoea from pleural effusion and/or abdominal distension from peritoneal effusion, although most dogs will present with chronic, nonspecific signs of illness. 

Carcinomatosis may occur through the dissemination of malignant epithelial cells through direct seeding of body cavity surfaces, lymphatic spread and haematogenous route.

What is the prognosis?

The prognosis for carcinomatosis (regardless of whether the origin of the primary tumour) is grave with most dogs humanely euthanised shortly after diagnosis.

The median (average) survival time in untreated dogs is about one month.

Unfortunately, this cancer is incurable and challenging to treat. However, treatment can significantly palliate clinical signs and quality of life, and in some cases, prolong survival. Moreover, the presence of an effusion is not necessarily associated with a worse prognosis.

What are the treatment options?

Intracavitary or Intravenous Chemotherapy

If the main concern is marked pleural and/or peritoneal effusion, then intracavitary chemotherapy is recommended to try to stop or slow down the rate of effusion.

Conversely, if the main concern is not malignant effusion, then I recommend injectable chemotherapy.

Intracavitary chemotherapy has a limited local penetration depth of 2 to 3 mm. Therefore, it is unlikely to work in larger or thicker lesions or nodules.

Chemotherapy drugs that could be considered include cisplatin, doxorubicin, mitoxantrone and carboplatin.

• In a small study of 12 dogs with carcinomatosis, mesothelioma and sarcomatosis, the median survival time of untreated dogs was about one month, compared to 11 months in dogs treated with intracavitary chemotherapy (with or without effusion). (Charney et al. VCO 2005)

• In a more recent study of 34 dogs with mesothelioma, the median survival time in untreated dogs was one month, compared to just under eight months in dogs treated with intracavitary and/or intravenous chemotherapy. (Moberg et al. VCO 2021)

• There are also case reports of dogs that can respond well to treatment, and the longest reported survival time in a dog with this approach was more than three years.

• Intracavitary cisplatin has also be reported to palliate six dogs with thoracic or abdominal mesothelioma or carcinomatosis. Complete remission was achieved in five of six dogs, with survival times ranging from 129 to >809 days. (Moore et al. JVIM 1999) Because of the higher toxicity profile and complexity with administration of cisplatin chemotherapy (i.e. aggressive saline diuresis), I tend to reserve cisplatin for when carboplatin and mitoxantrone fails to help.

Palladia®

Palladia® (toceranib phosphate) is an oral anticancer drug (multiple receptor tyrosine kinase inhibitor) that is administered at home on Monday, Wednesday & Friday with food.

In a recent retrospective study evaluating 23 dogs with carcinomatosis (60.8%, n =14) or mesothelioma (34.8%, n = 8) treated with Palladia®, one in three dogs responded to therapy. While most of the remaining dogs did not respond to therapy, they experienced stable disease, meaning the cancer did not progress. The median survival time for all dogs treated with Palladia® was about ten months. However, dogs with effusion had a lower median survival time of approximately 5.5 months. Most dogs (73.9%) experienced mild gastrointestinal side effects, with diarrhoea and hyporexia being the most common side effects. However, most of the gastrointestinal side effects resolved with a short break from Palladia®, dosage reductions, and supportive care medications. Rarely, does Palladia® side effects lead to discontinuation of therapy. (Hicks et al. VCO 2024)

Supportive Care

Anti-nausea, appetite stimulants, gastroprotectants, pain relief and anti-inflammatories are some supportive care medications that can be used in dogs with carcinomatosis.

Sick dogs may benefit from steroid anti-inflammatories (e.g. prednisolone), which can make dogs feel better within one to two days.

Vets, I hope this information helps you understand a bit more about the prognosis and treatment options for dogs with carcinomatosis. If you have a question about canine carcinomatosis or have a case that you would like evaluated, please do not hesitate to get in touch by clicking here.