Educating the Veterinary Students of Tomorrow


What is Chemotherapy in Animals?

Chemotherapy in animals is not usually used as a sole treatment, however it can be. Most often though it will be combined with other treatment modalities such as surgery and/or radiation therapy.

Metastasis and severity serve a role in selection of candidates for chemotherapy. Chemotherapy tends to be recommended for metastatic disease, multi-centric (those at multiple sites) or tumours that are not eligible for surgical removal. In certain circumstances, chemotherapy can be the primary treatment to help shrink down the tumour before the secondary treatment of surgical removal (Veterinary Hospital of the University of Pennsylvania (VHUP), 2013).

How Does it Work?

Chemotherapy targets cells that undergo rapid growth and division by the nature of neoplastic cells. Individual drugs differ on their mechanisms of action but in summary most interact with the neoplastic cells genetic DNA by preventing division.
The format in which these drugs are given can vary. Oral pills are an option, or slow infusions which require hospitalisation. These treatments are often repeated weekly to every 2-3 weeks.
The issue with chemotherapy is that drugs are unable to distinguish a normal cell from that of a malignant neoplastic cell. So, in theory all rapidly dividing cells are potentially sensitive to chemotherapy. Moreover, this is where most chemotherapy side effects will originate from. In most tissues, there is continual growth and repair so once chemotherapy has stopped it is not likely that the injury is permanent (The Veterinary Cancer Centre , 2018).

The Side Effects

With all treatments and surgeries side effects come as an unwanted bonus. However, animals tend to experience much lower side effects due to the lower doses of the drugs used.
Toxic effects on the gastrointestinal tract result in depressed appetite, vomiting and episodes of diarrhoea. Their severity can vary as documented. Oral medication is often given alongside chemotherapy to prevent this side effects occurring.
Whilst on chemotherapy the white blood cell count will drop leading patients susceptible to secondary infection. The infection can come from the animal’s own body (commensal bacteria, GI or respiratory bacteria) (Clyde Vet Group Small Animal, 2011).

The End Goal

Often cancer in our animals cannot be cured, the goal is to improve a pet’s quality of life and extend if it is possible. It can help minimize discomfort caused by a tumour and extend the life expectancy with or without treatments.

Decisions for the use of chemotherapy vary massively on a case to case basis. It is down to owner availability, pet’s temperament and with a lot of veterinary treatment on financial constraints (Veterinary Hospital of the University of Pennsylvania (VHUP), 2013).


Clyde Vet Group Small Animal, 2011. http://www.clydevetgroup.co.uk/small_animal/newsletters/chemotherapy-in-animals.html. [Online]
[Accessed 6 February 2018].

The Veterinary Cancer Centre , 2018. Chemotherapy. [Online]
Available at: http://theveterinarycancercenter.com/resource-center/treatments
[Accessed 6 February 2018].

Veterinary Hospital of the University of Pennsylvania (VHUP), 2013. 
Available at: https://www.oncolink.org/cancers/vet/diagnosis-and-treatments/chemotherapy-in-veterinary-medicine
[Accessed 6 February 2018].