Causes
What is the cause of cancer?

The appearance of mutations/errors in cells can be the consequence of different factors. A gene can carry a certain hereditary mutation (which increases the risk of developing a certain tumor type), but environmental factors and hormones can also contribute to the development of a tumor.

Hereditary factors

In humans, certain mutations that increase the risk of developing cancer are known (eg being positive for the BRCA gene with breast cancer). In animals, this is actively researched. Many mutations are similar, but many others are not. Until now, no commercial tests exist to examine risk factors.

On the other hand, it is known in veterinary medicine that certain dog races have a higher risk than other to develop cancer of a certain tumor type (see race predisposition). Therefore, it is important as dog owner to be aware of diseases specific for the race. The more informed we are, the quicker anomalies can be detected and the higher the chances of survival are.

Environmental factors
Virus

In dogs, the papillomavirus is responsable for the formation of warts. Certain warts can transform into tumors (which are in general benign).

Chemical products

Just as in man, chemical products such as asbestos and cigarette smoke can lead to mutations in cells of dogs and cats. So far, few carcinogenes have been researched in veterinary medicine. A three to fourfold increased risk has been documented between the development of lymphoma and sinonasal tumors and tobacco smoke.

Biological factors
Radiation (X/UV)

Radiation can impact cells by damaging the DNA directly or indirectly by causing damaging reactions in the cells (such as free oxygen radicals). There is a greater risk that UV radiation damages the skin on parts of the body that are less hairy (such as ear borders and nasal plane). This exposure could lead to a squamous cell carcinoma (SCC).

When radiotherapy is used as treatment, the X-rays can lead to the formation of a new tumor in the treatment site years after treatment.

Hormones

Especially sexual hormones can play an important role in the development of tumors in dogs and cats. For example, the risk to develop a tumor of the mammary glands is higher in dogs and cats who are not neutered.

References
  1. Henry CJ, Macy DW. The Etiology of Cancer. Withrow and MacEwen's Small Animal Clinical Oncology, 5th edition, Chapter 1 (p 15-26).
  2. ​Butler MB, Bonnett BN, Rodney LP. Epidemiology and the Evidence-Based Medicine Approach. Withrow and MacEwen's Small Animal Clinical Oncology, 5th edition, Chapter 4 (p 72-79).