Breast cancer is the third most common cancer in cats and mainly affects females. Breast tumours in cats are usually malignant and are called mammary carcinomas or adenocarcinomas. They affect the mammy glands, resulting in an uncontrolled growth of abnormal cells with a range of serious side effects.
Breast cancer usually occurs in older cats between the ages of 10 and 12, but it can be diagnosed at almost any stage of a cat’s life. Cats have four pairs of breasts and the most commonly affected are the thoracic and inguinal. When one or more mammary glands on one side of the body are affected by cancer, this usually spreads into the nearest lymph nodes and metastasises. These tumours are very aggressive, which means they can spread through the lymphatic vessels to other breasts, and even reach breasts on the other side of the body through the cat’s blood vessels.
The main danger of breast cancer in cats is the tumour’s strong tendency to spread to the lungs as well as the lymphatic system, which enables further metastasis to organs such as the liver, the spleen, the pancreas, the central nervous system or the bones. Once the cancer metastasises the prognosis is usually very poor, since treatment is practically ineffective and will eventually result in organ failure—in particular lung failure—ultimately causing death.
It is not entirely clear what causes breast cancer in cats. Genetic factors and carcinogens, such as certain viruses and environmental pollutants, may be involved, but the most likely cause is hormonal. Females who haven’t been spayed at an early age have a 90% higher risk of developing breast cancer than those who were spayed when they were very young—who can be spayed even before their first heat.
When you suspect the presence of a breast tumourin a cat—usually because you can feel a nodule, one has grown so large you can see it, or it’s even ulcerated—it’s important to begin a diagnosis using cytology or a biopsy to figure out what type of tumour it is and what stage it’s at. An analysis and comprehensive examination of the patient should also be carried out in order to gauge their overall state of health. Recommended treatments will vary based on the clinical examination and additional tests conducted, but will usually consist of surgical extraction of the growth (a mastectomy), either alone or combined with chemotherapy depending on the individual circumstances. In some cases, radiotherapy is also recommended. It is worth noting that, generally speaking, treatments increase life expectancy by about a year, and many tumours recur. Indeed, it’s always important to consider the patient’s quality of life.
As we’ve seen, breast cancer is a very serious illness in cats. It often spreads, producing metastases, and treatment rarely results in a cure. That’s why the most important thing is to focus on prevention, by spaying females at an early age, and taking them for regular clinical tests and palpations at the vet. That way, if a node appears it can be removed early on, before it grows too large and starts to metastasise.