There are five mammary glands in a female dog. Most cases of mammary, or breast, cancer occur in the fourth or fifth glands, but it can potentially affect any of the five glands. Stages of breast cancer are determined by the location of the tumour and how far it has spread through the rest of the body (metastasis).
The end stages of mammary cancer include dogs who are suffering from large tumours or extremely invasive tumours, involvement of the lymph nodes, additional sarcomas and spreading to far portions of the body.
Swelling or abnormal growths that are irregular in shape or size are common symptoms. These growths may bleed or ulcerate and be accompanied by additional symptoms such as coughing, loss of appetite and difficulty breathing.
Several tests are required to determine if breast cancer is present and whether spreading has occurred. These tests can include a biopsy of the abnormal growth, a physical exam, X-rays, a urinalysis, various blood work and ultrasounds.
Treatment options for canine mammary cancer include surgical removal of the growths, chemotherapy, radiation therapy, anti-oestrogen therapy and ovariohysterectomy, which is spay surgery (if the dog has not previously been spayed).
While there is no way to fully prevent canine mammary cancer, spaying prior to two years of age can greatly reduce their risk.