Cancer in cats: neoplasms

Neoplasms, characterised by the abnormal and progressive growth of new tissue, are common in cats. The prevalence is around 34.79% in cats, especially in adulthood and regardless of breed, with a range of clinical signs that depend on the organs affected, according to a study conducted by Graf et al. in 2016.¹

Main types of cancer in adult cats

• Lymphoma: This is the most common neoplasm of the haematopoietic system in domestic cats, accounting for between 25% and 33% of all malignancies in cats.²
• Squamous cell carcinoma: This is the most malignant epithelial neoplasm reported in cats, responsible for 9–25% of feline tumours, according to research conducted by Filgueira et al. in 2017.³
• Mammary carcinoma: This is characterised by the presence of nodules or inflammation in one or more mammary glands, which usually spreads to adjacent lymph nodes and sometimes to the lungs. It is fairly common in unsterilised females and is the third-most common type of tumour in cats, with a prevalence of 12% according to Benavides Melo et al. in 2013.⁴
• Mast cell tumour: Mast cell tumours are single or multiple nodules that develop from mast cells. They are considered the fourth-most common tumour in cats, making up between 2% and 21% of skin tumours.⁵
• Adenocarcinoma: This malignancy affects the glandular epithelium, so it originates in cells that form the inner lining of the exocrine glands. It usually causes circumferential thickening of the intestinal wall, as noted by Rives et al. in 1997.⁶
• Osteosarcoma: This cancer mainly affects the bones of the limbs, spine and skull. It is one of the most painful and debilitating tumours suffered by cats and is the leading primary bone cancer, accounting for 95% of all bone tumours.⁷

Cancer in adult cats: aetiology

Most cases of cancer in cats have an unknown aetiology. Exposure to sunlight, for example, has been associated with a greater predisposition for squamous cell carcinomas. The use of a flea collar may increase the risk by up to 5 times.⁸

Infections also increase the likelihood of developing cancer. Feline leukaemia virus (FeLV), for example, is associated with a greater risk of cancer. Most cats with mediastinal lymphoma (73%) also have feline leukaemia virus according to a 2018 study by Hinostroza et al..⁹ Furthermore, feline immunodeficiency virus (FIV) infection elevates the risk of developing a lymphoma by almost 6 times, as reported by Carballes.¹⁰

Cancer in adult cats: diagnosis

In most cases, a physical examination is not enough to diagnose cancer in cats. Diagnostic tests such as ultrasound, X-rays and blood tests are necessary to confirm the presence of a tumour, plus its location and size. However, the most effective means of confirming the diagnosis is still a biopsy.¹¹

Sometimes samples can also be obtained by other techniques, such as cytology via a fine needle aspiration, scraping or cytocentrifuge.¹² Depending on the type of cancer and its location, more complex tests such as an MRI or CT scan may be necessary to detect brain tumours, for example.

Cancer in adult cats: treatment

• Surgery: Surgery is the technique of choice in most cases of cancer in cats, although it can be combined with other treatments to improve its efficacy.¹³
• Radiation therapy: This is recommended in well-defined tumours since it works by destroying cancerous cells and damaging the DNA of tumour cells to prevent them from reproducing. However, the animal’s immune system becomes more vulnerable to opportunistic diseases.¹⁴
• Chemotherapy: Used in cases of metastasis or infiltrative tumours that are difficult to reduce by other procedures. It is also a good complement to surgery. Cytotoxic drugs act by inhibiting cell growth and division, while various alkylating agents, antitumour and antineoplastic antibiotics interfere with DNA replication. There are also antimetabolites, which prevent DNA or RNA synthesis through enzyme inhibition, and alkaloids, which block cell division. 
• Immunotherapy: This treatment stimulates the cat’s immune system to fight against the cancer.¹⁵

​References:

1.Graf, R. et al. (2016) Swiss Feline Cancer Registry 1965–2008: the Influence of Sex, Breed and Age on Tumour Types and Tumour Locations. Journal of Comparative Pathology; 154(2-3): 195-210.

2. Esteban, D. (2008) Linfoma alimentario felino: inmunofenotipo, quimioterapia y evolución de 9 casos clínicos. Clínica Veterinaria de Pequeños Animales; 28(2): 109-114.

3. Pérez, A. (2020) Linfoma mediastínico en el gato: a propósito de un caso clínico. In: Axón Comunicación.

4. Tonelli, E. et al. (2011) Tratamiento tópico del carcinoma de células escamosas (CCE) cutáneo felino en forma tópica con 5 fluoruracilo (5 FU): Descripción de un caso clínico. Revista Veterinaria Argentina; XXVIII (276).

5. Benadives, C.; Chaves, C. & Montenegro, J. (2013) Carcinoma tubulopapilar de glándula mamaria en un felino: reporte de caso. Revista de Medicina Veterinaria, 26: 123-132.

6. Rivers, B.; Walter, P.; Feeney, D. & Johnston, G. (1997) Ultrasonographic features of intestinal adenocarcinoma in five cats. Veterinary Radiology & Ultrasound; 38 (4): 300-306.

7. Colegio Americano de Cirujanos Veterinarios (s/f) Tumores Óseos en Perros y Gatos. In: American College of Veterinary Surgeons.

8. Bertone, E.; Snyder, L. & Moore, A. (2003) Environmental and life style risk factors for oral squamous cell carcinoma in domestic cats. Journal of Veterinary Internal Medicine; 17(4): 557-62.

9. Hinostroza, E. et al. (2018) Respuesta a la quimoterapia contra linfoma mediastínico en un gato doméstico. Revista de Investigaciones Veterinarias del Perú, 29(4): 1548-1555.

10. Carballés, V. (2010) Masas mediastínicas en el gato: Diagnóstico y tratamiento. Charla impartida en el congreso de grupos de trabajo de AVEPA.

11. Sanz, L. & Molina, M. (2011) Neoplasias malignas felinas entre 2006 - 2010: Estudio retrospectivo. Hospitales Veterinarios; 3(4): 133-141.

12. Fernández, C.; Jiménez de la Puerta, J. y Aguilar, A. (2003) Citología cutánea veterinaria. Revista AVEPA; 23 (2): 75-87.

13. Hershey, A. et al. (2000) Prognosis for presumed feline vaccine-associated sarcoma after excision: 61 cases (1986-1996). Journal of the American Veterinary Medical Association; 216(1):58-61.

14. Rosselló, A. (2017) El carcinoma de células escamoso felino: la electroquimioterapia y otros tratamientos novedosos. University of Zaragoza (end of degree project)

15.  Álvarez, F. (2018) Inmunoterapia en oncología veterinaria. In: IM Veterinaria; 25: 62-65.