Mammary Gland (Breast) Cancer in Cats
What are mammary gland (breast) tumors?
Mammary glands are female organs that produce milk for feeding the young. Cats have 4 glands on each side, which are
drained by nearby lymph nodes in the armpit and the groin. In contrast to humans and dogs, at least 85% of feline
mammary tumors are malignant.


How common are breast tumors in cats?
Mammary cancer is the third most common cancer in the cat after blood cancers and skin tumors.  There appears to be
some evidence that domestic shorthair and Siamese cats have higher incidence of mammary cancer. Cases have been
reported in cats ranging from 9 months old to 23 years old, with an average age being 10-12 years old.

What are the symptoms of breast cancer in cats?
By the time the cat is brought to the clinic for examination, the mammary cancer is usually in an advanced stage. The
tumors may adhere to the overlying skin and are typically firm and nodular. Ulceration of the masses is present in about
25% cats and the involved nipples may be red and swollen, oozing yellowish fluid.

How is the diagnosis made?
The diagnostic procedures include physical examination to determine the number, site and size of primary tumors, blood
and serum chemistry profiles/urinalysis to evaluate the patient's overall health status, and X-rays/abdominal ultrasound to
look for potential spread to other organs. Because ~85% of masses will be malignant in cats, preliminary tissue biopsy is
usually not done and the cat is recommended for surgical treatment of the cancer. Collecting cells with fine-needle
aspiration for cytology evaluation is not a sensitive method to distinguish malignant from benign cells but may be useful in
this case as a way to try to rule out malignancy. During the surgery, a piece of the mammary tumor is sent to pathology for

What are the treatment options for breast cancer in cats?
The primary goal of surgery is to remove the tumor. It may be used alone or in combination with other modes of cancer
therapy such as chemotherapy. In contrast to dogs, most cats require a complete unilateral or bilateral mastectomy
(complete removal of mammary tissue either one or both sides where the mammary glands are located). Unilateral
mastectomy is usually performed if the tumor(s) are confined to one side whereas bilateral mastectomy is performed on
cats in which the tumors are present  in both sides.

The chemotherapeutic agents used in treatment of feline mammary tumors are doxorubicin and/or cyclophosphamide,
however, more clinical trials need to be conducted to truly assess which doses and combinations are the most effective in
increasing the cats' survival.

Radiation therapy
Currently, there is no evidence suggesting that the cats' survival improves after radiation therapy and it is not used
routinely for the treatment of feline mammary tumors.

How do I find a qualified veterinary oncologist?
To locate a qualified veterinary oncologist worldwide who can discuss with you appropriate cancer treatment plan for your
pet's cancer condition, please visit the "
Locate a veterinary oncologist" section.  

What are the treatment associated risks?
The risks associated with the surgical removal of the mammary tumors include rare complications such as anesthetic death
and infection.

Does cancer cause pain in cats?
Pain is common in pets with cancer, with some tumors causing more pain than others. In addition to pain caused by the
actual tumors, pets will also experience pain associated with cancer treatments such as surgery, radiation therapy or
chemotherapy. Untreated pain decreases the pet's quality of life, and prolongs recovery from the illness, treatment or
injury. It is, therefore, essential that veterinary teams taking care of pets with cancer should also play a vital role in
educating pet owners about recognizing and managing pain in their pets.

The best way to manage cancer pain in pets is to prevent it, a term referred to as preemptive pain management. This
strategy anticipates pain ahead of time and administers pain medication before the pet actually experiences pain, thus
ensuring the pet's maximum comfort. To learn more about how to recognize pain in pets with cancer and what cancer pain
management options are available for your pet, please visit the
Cancer Pain Management section.

Is nutritional support important for cats with cancer?
Cancer cachexia (a term referring to progressive severe weight loss) is frequently observed in pets with cancer. Pets with
cancer lose weight partly because of lack of appetite and partly because of cancer-induced altered metabolism. Some of
the causes for decreased appetite are related to the cancer itself (for example, the tumors may physically interfere with
food chewing and swallowing) and some may be related to the side effects of cancer treatment (for example, some
chemotherapy drugs cause nausea and vomiting, and radiation therapy can cause mouth inflammation).

Proper nutrition while undergoing cancer treatment is essential to maintain your pet's strength, improve survival times,
quality of life and maximize response to therapy. Adequate nutritional support was shown to decrease the duration of
hospitalization, reduce post-surgery complications and enhance the healing process. Additionally, pets with cancer need to
be fed diets specifically designed to provide maximum benefit and nutritional support for the patient. To learn more, please
visit the
Cancer Nutrition section.

Are there any clinical trials investigating new treatments for breast cancer in cats?
There are no available clinical trials investigating new treatments specifically for breast cancer in cats. However, there are
a few clinical trials available for cats with any tumor type for which your cat may qualify. To learn more these trials (which
are partially or fully funded by the institutions), please visit the
Cat Clinical Trials (any tumor type) section.  

To learn more about veterinary clinical trials in general, please visit the
Pet Clinical Trials section.

What is the prognosis for cats with breast cancer?
The prognosis of the cat will depend on several factors including tumor size, extent of surgery and histologic grade (level of
malignancy). It's been reported that cats with tumors larger than 3cm in diameter have a median survival time of 4-12
months, cats with tumors 2-3cm in diameter have a median survival time of 15-24 months, and cats with tumors smaller
than 2cm in diameter have a median survival time of longer than 3 years.

Additional Online Resources

  • Withrow Stephen J, and David M. Vail. Small Animal Clinical Oncology. St Louis: Saunders Elsevier, 2007.
  • Morrison Wallace B. Cancer in Dogs and Cats: Medical and Surgical Management. Baltimore: Williams&Wilkins, 1998
Comprehensive guide to cancer diagnosis and treatment in cats and dogs
© 2007 Pet Cancer Center. ALL RIGHTS RESERVED.
Last updated 2/19/2017