In cats and dogs, the mammary glands are located on both sides of the abdominal line as four pairs. They are not active in puppies/kittens and juveniles.

They start to grow by the effect of adolescence and mating in females via the effect of hormones. They are prepared during pregnancy in order to meet the breast milk, which is the nutritional need of the puppies/kittens after delivery. They become active after delivery and begin to produce milk. Mammary glands are under dense hormonal pressure during the postpartum and lactating periods. When the puppies/kittens start to eat additional foods, the milk in the mammary glands will not be needed. However, when milk not discharged from breast even though it is secreted remains in the breast, several risks also emerge. The remaining milk is often degraded by pathogenic microorganisms and causes local infections. Against this condition, also called as mastitis, local lymph nodes are swollen. In general, this situation that is confronted as a cold abscess and a cyst, is often among the causes of mammary tumors.

However, the causes, formations, and tissues of mammary tumors are different. The swellings seen in the mammary glands should not always be considered as mammary tumors.

Although the causes of mammary tumors are unknown, female sex hormones are thought to be effective. Breast tissue is sensitive to tumor formation 5 times greater than other organs related to reproduction. It is the most common tumor type in dogs after skin tumors. Female dogs aged between 5 and 10 years are prone to the disease more. In cats and dogs, mammary tumors can be seen in a single breast lobe and also it can be seen in all breast lobes at the same time.

Mammary tumors are the tumors which can spread directly to the mammary tissues from the primary tumor focus, either directly starting in the mammary gland or through metastasis (spreading). It appears in two different forms as malignant or benign. It is frequently observed in cats and dogs.

Benign tumors (hyperplasia) are not prone to spread. There is no ulceration, they can be moved under the skin and they are characterized by slow growth. Their contours are regular and evident.

Malignant tumors may spread to other organs of the body by making metastasis according to growth rate and character. Mammary tumors are more commonly seen in inguinal breast lobes. The possibility of malignancy is higher compared to other breast lobes. As the reason of this situation, it is shown that the duration of the milk secretion in these mammary glands is longer and slower. Malignant tumors can also metastasize to other lymph nodes in the body via lymph fluid and the blood route. Malignant tumors have ulceration, their contours are unclear, they have an inflammatory structure, color changes can be seen, they do not move under the skin and they adhere to the skin.

Reasons of Mammary Tumors in Cats and Dogs:

  • Gender: Female pets are much more susceptible to mammary tumors than males.
  • Genetic factors: Susceptibility and tendency of the patients with cancer histories in their family backgrounds is a known fact. Likewise, cancer in the pets is genetic-based.
  • Breeds: Researches show that small-breed dogs are more susceptible to the disease than large breeds. Moreover, Siamese cats are more susceptible to the disease than other cat breeds.
  • Drugs: It is thought that long-lasting hormone medications and synthetic hormones used in pregnancy control cause the formation of mammary tumors.
  • Endocrine System Disorders: Hormonal disorders, ovarian cysts, and pseudo-pregnancies cause mammary tumors because they suppress hormone metabolism for a long time.
  • Milk Deposition in Breast: Milk deposition in breast causes swellings in local lymph nodes and unwanted cystic formations in the breast tissue due to the fact that the puppies/kittens are not fed adequately from the mother after birth because of various reasons (death of the puppy/kitten, premature separation from the mother, etc.). These tissues can eventually turn into tumoral formations.
  • Stress: Although it cannot be proven, there are opinions indicating that birth process and stress of the mother after birth will cause hormonal changes and this triggers the mammary tumors.
  • Nutrition Disorders:  In addition to malnutrition, overfeeding is among the reasons of mammary tumors. Mammary tumors are more prevalent in overweight and obese pets as they are seen in weak pets.

Symptoms of the Disease

Although mastitis, abscess, lipomas, and cystic formations can be confused with mammary tumors, enlargements related to the infections in lymphatic nodules can also be confused with mammary tumors. In mastitis and abscess; redness and swelling on the breast tissue, and usually general condition disorder are seen. Inflammatory and bloody discharge comes from the nipple. Local lymph nodules are swollen. Septisemi picture develops in the patient. This can be suppressed by using strong antibiotics and anti-inflammatory agents. However, it should be kept in mind that in addition to the cystic connective tissue or cold abscess forming in the breast tissue, swollen lymph nodes may become tumorous in time and are a problem.

In malignant mammary tumors; loss of appetite, fatigue, pain, and swelling are observed as clinical symptoms. A painful lump integrated with the breast tissue is identified. Sometimes, these tumors can also become suppurating. In this case, there is a bloody inflammatory discharge coming from the nipple. In the clinical examination; it is observed that local lymph nodes are swollen and they arise in the form and size of marbles. Their sizes may vary. A rapid growth is seen in malignant tumors.

In the examination, benign tumors are more uniform and round in shape. Malignant tumors are amorphous and massive.

Mammary tumors cause negativities by affecting or limiting the quality of life of the patient.


In the treatment; chemotherapy, radiotherapy, immunotherapy and surgical operation methods are applied. The mostly preferred method in the early period is operation. The operation should be performed over the healthy tissues as much as possible. Local lymph nodes can also be taken together with lump with the lesion. The part taken via operation or biopsy must be absolutely sent to pathological examination. This is important for follow up of the patient and planning the treatment. According to the pathologic results, chemotherapy and immunotherapy should be performed after the operation.

Medication can be effective in mastitis and in open-ended abscess. However, the resulting cystic tissue and non-recoverable lymph nodes have to be removed by a surgical operation over time.

Points to Take Into Account Before the Operation

The appropriate time for the operation should be decided together by the patient owner and the veterinary physician. Then, the general health controls of the patient should be done for the operation. These examinations will be useful in order to determine the general condition of the patient and not to pose a risk in the patient to be anesthetized. Thus, ultrasound and blood tests should be performed for the patient. Tumors in the mammary gland may spread to the lymph nodes, brain, chest, bones, and spleen. Preoperative chest radiography should be taken in order to determine whether the tumor spreads to the lungs or not.

If the patient has any drug allergy, this should absolutely be shared with the veterinary physician.

The patient should not be fed within 12-24 hours before the operation. This approach will allow the patient, to be anesthetized, to undergo a more comfortable operation.

Technique of the Operation

Sterilization processes of the patient to whom a sedative is administered for the operation, are performed in the preparation room. First of all, the hairs on the operation area are shaved. Then, the area is disinfected with an antiseptic solution. Anesthesia preferred by the veterinary physician is applied to the patient who is taken to the operating room. The area is limited by a sterile cloth and made ready for the surgical intervention.

The operation area is the mammary gland with the tumor and its surrounding tissue. The tumoral mass is reached after the skin is incised. It is important to note that the tumoral tissue must be removed completely. Since tumors are very bloody tissues, the physician should be careful about the hemorrhage during the operation. Thus, the operation area should be kept as wide as possible, and the operation should be carried out through healthy tissues. Because even small parts remaining from the tumoral mass are the cause of metastases and relapses. Veins between the mammary glands facilitate the spreading of tumor cells, so the operation should be performed on not only the affected breast lobe but also all the mammary glands on the same side. If tumors develop on both sides, the whole mammary glands should be removed.

Hormones have an important place in the formation and relapse of mammary tumors. Thus, an ovariohysterectomy operation can be considered during the mammary tumor operation.

Afterwards, the muscles and skin are closed and the operation is completed.

Points to Take İnto Account After the Operation

The antibiotics administered after the operation should be of the duration and dose recommended by the veterinary physician. WinPet Wound Protecting Corset should be absolutely used as the patient will harm the operation area by licking and biting (See Video). Sudden movements that may create a risk such as jumping should be avoided.

Pain killers can be used when needed.

Complete recovery is completed within about 10-12 days and sutures can be removed.

If there is a condition such as swelling, redness, inflammation etc. occurs due to a possible edema in the region in this period, the veterinary physician should be consulted as soon as possible.

Possible Complications After the Operation

Complications that may develop are scarcely any provided that necessary sterilization and the use of suitable materials during the operation and regular administration of antibiotics after the operation are taken into consideration.

However, excessive and inappropriate exercises should be avoided in the recovery period and sutures should be protected. WinPet should not be removed during the recovery period. Otherwise, eventration can occur (opening of the sutures and protrusion of viscera)

The most important complication after the operation is the relapse possibility of the tumor in the future. Therefore, the patient should be kept under control periodically.


The most important protection for female pets is early spaying. Spaying operations before puberty reduce the risk of mammary tumor to a great extent. Spaying in pets older than the age of 2 and giving birth at least once is scarcely any in protection from mammary tumors.

Early diagnosis and treatment are very important in dogs and cats. Owners of female cats-dogs should manually examine the mammary glands every 3 months and if any change is noticed in the mammary glands, the veterinary physician should absolutely be consulted. Mammary tumors may occur in size and shape of marbles or large and irregular shaped masses. Local lymph nodes due to the tumor may also be noticed by palpation examination.

Recent researches have revealed that the long-term administration of hormone drugs triggers mammary tumors. Thus, long-term use of hormone drugs should be avoided. Operative spaying methods should be preferred in the control of the reproduction.

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