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Stages of Breast Cancer in Cats - Mammary Tumors in Cats

Laura García Ortiz
By Laura García Ortiz, Veterinarian specialized in feline medicine. January 10, 2021
Stages of Breast Cancer in Cats - Mammary Tumors in Cats
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Have you noticed an unusual lump on your cat's belly? Whether it is just one lump or more than one, this is one of the most common symptoms of mammary tumors in cats and should be taken very seriously. In this AnimalWised article we're going to explain the different stages of breast cancer in cats, as well as symptoms, causes, treatment and more.

If your cat is experiencing one or more of the symptoms we share below, they may be suffering from a mammary tumor and will need immediate attention from your trusted veterinarian. Keep reading to learn more.

You may also be interested in: Breast Cancer in Dogs - Symptoms and Treatment
  1. Mammary tumors in cats
  2. Causes of mammary tumors in cats
  3. Symptoms of breast cancer in cats
  4. Diagnosis of mammary tumors in cats
  5. Treatment of mammary tumors in cats
  6. Prognosis of mammary tumors in cats
  7. Prevention of breast cancer in cats

Mammary tumors in cats

Mammary tumors in cats, also known as breast cancer in cats, occur when normal cells in the mammary gland transform into tumor cells that can multiply and invade nearby or distant tissues by hematogenous or lymphatic routes.

This type of cancer is actually the third most common in cats, preceded by lymphoma and skin tumors. Mammary tumors can be benign (non-cancerous) or malignant (cancerous). Each of them will have different diagnostics, treatments, management, and prognosis. alignant are much more frequent than benign, with a percentage of 90% of all cancer in cats and a high mortality rate.

Furthermore, around 35% of breast tumors at the time of diagnosis already have metastases in nearby tissues. This metastasis can occur at a distance, affecting various organs. However it is more common to infect the lungs. In fact, more than 80% of the time, the cancerous cells reach the lungs.

For more information, you can read our article about cancer in cats.

Stages of Breast Cancer in Cats - Mammary Tumors in Cats - Mammary tumors in cats

Causes of mammary tumors in cats

Although the exact cause for the development of mammary tumors in cats isn't fully understood, we do have an understanding of what factors play a role in its development. The main causes of mammary tumors in cats include:

  • Genetics: for examples, siamese cats have twice the risk of suffering from breast cancer.
  • Hormones: breast tumors are hormonally dependent, which means that most have receptors against estrogens and progestogens, hence early sterilization is the best prevention.
  • Obesity: this can also play a role when a cat is diagnosed with mammary tumors. Learn more in our article about obesity in cats.
  • Age: this can also play a factor as mammary tumors in cats are often seen in middle aged to older cats.
  • Spayed/neutered: cats that have been spayed or neutered at a young age have lower chances of developing tumors.

With that being said, if your cat hasn't been spayed or neutered by the age of 6 months, is a siamese a cat or is obese, they are now in a much greater risk of developing mammary tumors. We must also keep in mind that breast cancer in female cats is much more serious and fatal than in male dogs.

Symptoms of breast cancer in cats

The clinical signs of mammatory tumors in cats include:

  • Lump in one or more breasts
  • Growth of these lumps
  • Ulceration of tumors
  • Breast infections
  • Lung or other organ conditions worsen (if the tumor has spread)
  • Weight loss
  • Weakness

As we have previously mentioned, mammatory tumors are more serious in female cats than in males. Female cats have a total of eight breasts divided into two cranial and two caudal nerves. Breast tumors can appear in isolation in a single, well-defined, and mobile mass or an infiltrative-like growth to deep locations that have the potential to ulcerate and cause secondary infection.

It is also common for the same affected breast to have multiple nodules and for several breasts to be affected by the cancerous cells. In fact, around 60% of female cats have more than one tumor when diagnosed. Nearby lymph nodes are also often affected.

Look at the photo below to see what breast cancer in cats looks like. If you see that your cat has one or various lumps on their breasts, it's very important for you to take them to the veterinarian as soon as possible.

Stages of Breast Cancer in Cats - Mammary Tumors in Cats - Symptoms of breast cancer in cats

Diagnosis of mammary tumors in cats

The usual diagnostic procedure for this disease includes blood tests, urine tests, and chest X-rays. Due to the fact that it normally occurs in older cats, it is also important to measure T4 to see the status of their thyroid glands.

Although the vast majority of breast tumors in cats are malignant, before the previously described mammary lesions, a differential diagnosis must be made with other pathologies that non-castrated cats may present, such as fibroadenomatous hyperplasia, pseudopregnancy and gestation.

Stages of breast cancer in cats

The feline breast tumor staging system is based on the size of the primary tumor by measuring the diameter of the mass (T), the involvement of nearby lymph nodes (N) and the metastasis in distant organs (M).

All the mammary glands and surrounding tissue should be palpated, regional lymph nodes palpation and cytology, chest radiographs performed in various projections to assess for possible lung metastasis, and abdominal ultrasound to assess abdominal organ metastases. The stages of breast cancer in cats are:

  • I : lumps less than 2 cm (T1).
  • II : 2-3 cm lumps (T2).
  • III : lumps larger than 3 cm (T3) with or without regional metastasis (N0 or N1) or T1 or T2 with regional metastasis (N1).
  • IV : distant metastasis (M1) and the presence or absence of regional metastasis.

Treatment of mammary tumors in cats

Due to the fact that adenocarcinomas in cats is invasive and has a high rate of lymphatic involvement, aggressive treatment is required in order to combat this health issue.

This treatment will consist of a breast removal surgery, also called a mastectomy, that can be complemented with chemotherapy and radiation therapy. Radiation therapy is a local treatment that in cats can be effective in preventing tumor recurrence.

Surgery for mammary tumors in cats

Mastectomy in cats is more aggressive than in the canine species, because it must be performed on the entire affected mammary chain. It is contraindicated only when the disease is very advanced and there are already distant organ metastases, so a complete mastectomy will be performed on one side if the affected breasts are in a single chain or complete bilateral if the affected breasts are distributed by both chains mammary. In addition, it must be completely removed with wide margins that are key to reducing the recurrence of cancer in the area and increasing survival times.

The affected lymph nodes should also be included in the mastectomy. The inguinal is removed next to the caudal mammary gland and the axilla is removed only if it is enlarged or metastasis has been detected on cytology. Once extracted, samples must be taken to send to histopathology to diagnose the type of tumor that the cat has.

In the postoperative period of mastectomy in cats, analgesics and antibiotics are necessary to control pain, inflammation and possible infections produced. The first week is the most painful, especially the full bilaterals. It may take your cat several days to feel better and have an increase appetite and vitality. They should be put on an Elizabethan collar so that they do not lick the area and open the stitches. On the other hand, possible complications are:

  • Pain
  • Inflammation
  • Infection
  • Necrosis
  • Self-trauma
  • Broken sutures
  • Swelling of the hind limb

Stages of Breast Cancer in Cats - Mammary Tumors in Cats - Treatment of mammary tumors in cats

Chemotherapy for mammary tumors in cats

Based on the principles of oncology, adjuvant chemotherapy is recommended in cats with clinical stages III and IV or in cats in stage II or III malignant tumors. It is performed after the tumor removal to delay recurrences, lengthening the remission period and delaying the appearance of metastasis. It is usually administered every 3-4 weeks, making it a total of 4-6 cycles. Side effects that may appear in a cat undergoing chemotherapy will be: anorexia, anemia and a decrease in white blood cells due to myelosuppression.

Your veterinarian may also decide to add a non-steroidal anti-inflammatory drug (NSAID) that inhibits cyclooxygenase type 2 (COX-2), such as firocoxib or meloxicam, since these tumors have been shown to express COX-2. Lastly, different chemotherapy protocols have been described for feline mammary tumors, for example:

  • If we are dealing with stage III or IV breast cancer: doxorubicin (20-30 mg / m2 or 1 mg / kg intravenously every 3 weeks) + cyclophosphamide (100 mg / m2 for 3 days every 3 weeks orally).
  • With surgery + carboplatin (200 mg / m2 intravenous every 3 weeks, 4 doses) studies demonstrated a median survival of 428 days.
  • Cats with surgery and doxorubicin in tumors smaller than 2 cm demonstrated a median survival of 450 days.
  • With surgery and doxorubicin, a survival of 1998 days.
  • With surgery, doxorubicin and meloxicam, a survival of 460 days was observed.
  • With surgery and mitoxantrone (6 mg / m2 intravenous every 3 weeks, 4 doses) a survival of 450 days was determined.

Treatment is usually accompanied by nutritional supplements, antiemetics and appetite stimulants for the prevention of weight loss and to remedy the symptoms. At the same time, if the cat has some type of organic failure, it must be treated.

Prognosis of mammary tumors in cats

The median survival time from diagnosis to death of the cat is 10-12 months. Early diagnosis and early mastectomy are key factors in extending survival time. TO have a better idea about the median survival time you can take a look at our graph below, however, only your veterinarian will be able to tell you with greater certainty:

  • Cats with tumors larger than 3 cm in diameter have a median survival time of 4 to 6 months
  • Cats with tumors 2 to 3 cm in diameter have a median survival time of about 2 years
  • Cats with tumors less than a 2 cm in diameter have a median survival time of over 3 years

The prognosis will always be worse the larger the diameter of the tumor. Those with a small diameter will show longer periods of remission and longer survival time. The presence of distant metastases is always indicative of a poor prognosis.

This way, if you notice any change in your cat's breasts, you should go to the veterinarian to find out as soon as possible if you are dealing with breast cancer or another mammary pathology. As we have previously mentioned, the progression of malignant breast cancer is devastating, since in most cases it will invade the lungs of our cat, making it difficult for them to breathe correctly, affecting other vital organs, leading them to their death.

Stages of Breast Cancer in Cats - Mammary Tumors in Cats -  Prognosis of mammary tumors in cats

Prevention of breast cancer in cats

The best prevention of breast cancer in cats is an early sterilization before their first heat (before they are 6 months old) because it will greatly reduce the chances of suffering from it. This is essential, since the life expectancy of a cat with breast cancer is very low, even with treatment.

If your cat is sterilized after the first year of life, they will avoid other health issues, such as pyometras, metritis and ovarian or uterine tumors. Early sterilization considerably reduces the future presentation of breast cancer in cats, so much that:

  • It decreases by 91% if it is done before 6 months, that is, they will have only a 9% chance of suffering it.
  • After the first heat the probability will be 14%.
  • After the second heat the probability will be 89%.
  • After the third heat, the risk of breast cancer is not reduced.

Other than early sterilization, you must simply provide your cat with a happy and healthy life. This includes high quality cat food, an active lifestyle, minimum stress, lots of attention and affection too. You must also keep up with their deworming schedule and vaccination schedule, as well as their regular veterinarian check-ups.

You may also want to see our video about how to tell if your cat is dying.

This article is purely informative. AnimalWised does not have the authority to prescribe any veterinary treatment or create a diagnosis. We invite you to take your pet to the veterinarian if they are suffering from any condition or pain.

If you want to read similar articles to Stages of Breast Cancer in Cats - Mammary Tumors in Cats, we recommend you visit our Other health problems category.

  • JC Cartagena. (2011). Veterinary Oncology. SERVET editorial, Grupo Asís Biomedia SL
  • N. del Castillo, AVEPA. (2019). Mammary tumors in the cat. https://www.avepa.org/pdf/vocalias/tmf_2019.pdf
  • SJ Ettinger, FC Feldman. (2007). Treaty of veterinary internal medicine. Elsevier Saunders.
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Stages of Breast Cancer in Cats - Mammary Tumors in Cats