Breast or mammary cancer is one of the most common cancers in dogs, especially in female dogs. Find out the various types of mammary tumors in dogs, the symptoms, causes, and risk factors, in this DogAppy article.
Did You Know?
Spaying a female dog can reduce the risk of mammary cancer by more than 98%, provided it is done before she goes into her first heat cycle. If spaying is done before the second heat, then the risk of developing breast tumors is about 8%.
When it comes to human breast cancer, a lot of awareness has been created in the recent times. But, dogs can get breast cancer too. As per estimates, incidence of breast cancer in dogs is higher than humans and surprisingly, not many pet owners are aware of this. It has been found that one out of every four unspayed female dogs can develop cancerous tumors in their mammary glands. Breast cancer in dogs is usually called mammary cancer.
Mammary tumors are the most common types of tumors in female dogs, especially the unspayed female dogs between 5 to 10 years. Sometimes, male dogs can also develop this cancer, in which case the disease can be quite aggressive. By knowing the causes and symptoms of mammary cancer, as well as the preventive measures, you can protect your dog from this life-threatening condition.
Types of Mammary Cancer in Dogs
Dogs can develop several types of mammary tumors, out of which 50% are benign, while the rest 50% can be malignant. Usually, a benign mammary tumor can be a mixture of different types of cells, out of which one cell can become cancerous at times. Other types of benign tumors that are commonly observed in dogs are, adenomas, complex adenomas, duct papillomas, and fibroadenomas.
On the other hand, the most common types of malignant mammary tumors are, papillary cystic adenocarcinomas, tubular adenocarcinomas, papillary adenocarcinomas, solid carcinomas, fibrosarcomas, anaplastic carcinomas, and malignant mixed tumors.
Causes and Risk Factors
» The development of benign mammary tumors in dogs is suspected to have an association with the sex hormones, progesterone and estrogen. These hormones may cause some mammary cells to grow abnormally, and such cells can become more susceptible to malignancy when they get exposed to certain environmental carcinogens. This may explain why some benign growths become malignant later.
» Moreover, about 50% of the canine mammary tumors, including the benign tumors have been found to contain receptors for estrogen or progesterone. This means that these sex hormones can play a role in increasing the size of the tumors.
» It has been observed that the risk of developing both benign and malignant mammary tumors significantly decreases when female dogs are spayed before they turn 2.5 years old. Spaying after this age can reduce the risk of benign tumors but does not ensure the prevention of malignant tumors.
» The incidence of mammary tumors is quite rare in dogs that are spayed before they reach the age of 2 years. On the other hand, the unspayed middle-aged dogs between 5 to 10 years are at an increased risk of developing tumors in the mammary glands.
» Certain breeds such as Poodle, English Setter, Boston Terrier, Fox Terrier, Cocker Spaniel, and Brittany Spaniel are at a higher risk of developing this cancer.
Signs and Symptoms
Usually, there are 8 to 10 mammary glands in a female dog, that are arranged in two rows, going down the length of the body from the armpits to the groin area. Cancer can develop in any one or all the mammary glands but mostly it affects those closer to the hind legs. The most common signs and symptoms that are associated with mammary tumors are:
✦ Small lumps or nodules in the tissues of the mammary gland.
✦ Lumps with irregular shapes that remain attached to the skin or the underlying tissue.
✦ Bloody, straw-colored, or pus-like discharge from the nipples.
✦ Lumps or growths that become inflamed or ulcerated.
✦ Larger and deeper protruding growths in the mammary tissue.
✦ Stiffness, loss of appetite, and weight loss.
Diagnosis and Treatment
A needle aspiration is usually carried out as a part of preliminary investigation. It helps determine whether a tumor is benign or malignant, and decides how aggressive should be the surgical procedure. But for an accurate diagnosis, biopsy is required. It helps detect the stage of the disease, the type of the tumor, and whether it is benign or malignant.
As far as the treatment is concerned, most dogs with mammary cancer require surgical removal of the tumor. Sometimes, the entire mammary tissue along with the lymph nodes have to be removed to treat this cancer. Dogs with low histologic grade carcinomas and adenocarcinomas can be treated surgically, if the cancer has not spread to other parts of the body. As a large majority of the mammary tumors contain estrogen or progesterone receptors, many veterinarians suggest spaying the affected dog before or at the time of surgery. Doing this has been found to have a positive effect on prognosis.
Usually, prognosis is good when the cancer is detected in the early stages. Along with the stage, the size of the tumor is another factor that determines the prognosis of mammary cancer. It has been observed that dogs with small tumors, usually smaller than 3 cm in diameter, have a better prognosis than dogs with large tumors. This is because, large tumors are more likely to metastasize or spread to other parts of the body.
How to Check Your Dog for Mammary Tumor
✦ As mentioned already, there are usually 8 to 10 mammary glands in dogs. To check for the presence of lumps in the mammary glands, run your hands under the belly of your dog. Press the area gently to feel for any unusual growth or lump.
✦ Then check the armpits and the groin area. While doing so, try to feel for any lump or nodule.
✦ Now examine each mammary gland by gently pressing it with your fingers. If you detect any abnormal growth in the area, get your pet immediately evaluated by a veterinarian to find out whether the tumor is benign or malignant.
Mammary cancer in female dogs can be prevented to a great extent by spaying them before they go into heat for the first time, which usually happens when they are about 6 months old. As the spaying age increases, the protection offered by this process reduces. So, talk to your veterinarian about spaying your dog, and the risks and benefits associated with the procedure. Even if you have spayed your dogs, do not forget to check them regularly for the presence of any abnormal growth and lumps. If you detect such growths, get them evaluated by a veterinarian at the earliest.
Disclaimer: This article is for informative purposes only, and should not be treated as a substitute for professional medical advice.