Canine Breast Cancer

"Canine breast cancer are referred to as neoplastic malignant mammary gland tumors (MGT), which means that they are cancerous and growing uncontrollably. Mammary tumors in dogs are among the most common type of tumor found in intact female dogs. Approximately 50% - 71% of canine mammary tumors are cancerous, with the other 50% being considered benign or not life threatening. A dogs prognosis (expected life expectancy is based on the nature of the tumor including the tumor size, whether the cancer has spread to nearby lymph nodes and other areas of the body (metastasis), how deep the tumor is into the tissue and the presence of estrogen receptors (estrogen receptors in cells can change cell behavior). If tumors are diagnoses early, and can be successfully removed with surgery, the prognosis is excellent. A veterinarian may recommend other therapies along with surgery including chemotherapy.""

Canine Breast Cancer is the most common type of cancer in female dogs. Female dogs have five pairs of mammary glands with the possibility of tumors forming in any one of the glands. Breast cancer can spread from one glad to another. Spaying a female dog dramatically reduces the odds of getting breast cancer if done early in the dog’s life.

Canine breast cancer represents 52% of tumors found in female dogs and are seen in dogs that are between the age of 10 and 11. Half of the dogs with mammary gland tumors will have multiple tumors. Most dogs with a tumor will see the cancer spread to the lungs in 1 to 2 years.

Breeds that are Susceptible to Canine Breast Cancer or Mammary Cancer

  • Spaniels
  • Terriers
  • German Shepherds
  • Toy and Miniature Poodles

Picture of Dog Breast Cancer
Inflammatory Mammary Carcinoma in Dog

canine breast cancer picture

Diagnosis of Canine Breast Cancer or Canine Mammary Cancer

Your veterinarian will look for visible signs of canine breast cancer or mammary cancer tumors. Signs can include swelling, or soft or hard lumps near the mammary glands. If tumors are not visible, diagnosis is made when other symptoms are investigated and a tumor is found to be the cause.

A Fine Needle Aspiration (FSA) test or biopsy is used to take a tissue sample for testing prior to the recommendation of surgery. Though rare, a tumor may look like cancer when in fact it is a benign cyst. The FSA test will allow for a definitive diagnosis.

Other necessary tests include a CBC, chemistry profile, urinalysis and
3-view thoracic X-Rays, which help the veterinary oncologist check if the disease has spread. 

Treatment of Canine Breast or Mammary Cancer

Surgery is the most common form of treatment for breast cancer that has not spread (lumpectomy, mammectomy, mastectomy). Localized cases use surgery as a complete cure, the case if the tumor is small and the margins or the tumor are easily identified and removed. Chemotherapy is used in more advanced cases.  Surgery is recommended in cases where the cancer has spread to the lymph node.

Consult your veterinarian if you see any lumps near the mammary glands. It is possible that tumors are benign (non cancerous). If this is the case, most veterinarians will remove the tumor and then send to a lab for a definitive evaluation.

In addition to surgery, your veterinarian may recommend chemotherapy treatment to make sure that malignant cells (cancer cells that spread quickly) do not spread to the lungs. Chemotherapy drugs such as Adriamycin and oral Cytoxan are used. Recently other drugs such as mitoxantron (Novantrone™) and Adriamycin or Carboplatin (if other drugs are proving to be ineffective) have been used. One study shows that the  2-year survival rate for 8 dogs treated with surgery alone was 29% while the survival rate for 8 dogs treated with the chemotherapy medications adjuvant 5-fluouracil and cyclophosphamide was 100%.3

Chemotherapy usually lasts for a span of 6 months with the number of treatments defendant on the severity of the disease (possibly 4 to 6 per week).

Another approach to possibly extend an intact female dogs life with canine breast cancer is not not only have the malignant tumor removed surgically, but to undergo  an Ovariohysterectomy (OHE).   Recent studies have shown that the benefit could result in a 45% increase in the length of survival after treatment1.

Other approaches that are dependent on tumor type and that should be discussed with your veterinarian include Radiation Therapy, Estrogen Therapy and the use of Cox-2 Inhibitors

Common supplements that may contribute to a reduced the risk of breast cancer include Inositol hexaphosphate and 1-3-beta glucan. Natural remedies such as C-Caps may be of some help as a supportive therapy during and after treatment to strengthen healthy cells and reduce the severity of symptoms. If your dog is recieving chemotherapy or  radiation be sure to check with your veterinarian since anti-oxidants and certain supplements may inhibit these types of drugs since they strengthen all types of cells, even those that may be targeted by treatment.

For dogs with large breast tumors (> 3.0 cm), the prognosis tends to be poor since there is an 80% chance of recurrence of the tumor within 6 months after canine breast cancer treatment. The survival rate of dogs with what is termed gross metastasis or widespread spreading of cancer is 5 months.  The overall rate of 2 year survival is between 75% and 90%2.


1. Sorenmo KU, Shofer FS, Goldschmidt MH. Effect of spaying and timing of spaying on survival of dogs with mammary carcinoma. J Vet Intern Med. 2000;14:266-

2. Yamagami T, Kobayashi T, Takahashi K et al. Influence of ovariectomy at the time of mastectomy on the prognosis for canine malignant mammary tumours. J
Small Anim Pract. 1996;37:462-464

3. Karayannopoulou M, Kaldrymidou E, Constantinidis TC et al. Adjuvant post-operative chemotherapy in bitches with mammary cancer. J Vet Med A Physiol Pathol Clin Med. 2001;48:85-9

How I Treat Canine Mammary Gland Tumors
Kenneth M. Rassnick, DVM, DACVIM
College of Veterinary Medicine
Cornell University, Ithaca, NY

World Small Animal Veterinary Association World Congress - 2001

Campos C.B., Lavalle G.E., Bertagnolli A.C., Tavares W.L.F. & Cassali G.D.
Laboratório de Patologia Comparada – Departamento de Patologia Geral – ICB/UFMG Caixa Postal

Kerstin U. Honscha1, Arite Schirmer1, Christiane Herfurth1, Anne Reischauer³, Heinz-Adolf Schoon, Almuth Einspanier², Gotthold Gäbel
1Veterinär-Physiologisches Institut, Universität Leipzig, An den Tierkliniken 7, 04103
Leipzig; ²Veterinär-Physiologisch-Chemisches Institut, Universität Leipzig; ³Institut für Veterinär-Pathologie, Universität Leipzig

Canine Cancer Awareness

James M. Giffin MD and Liisa D. Carlson DVM; Dog Owner’s Home Veterinary Handbook

Washington State University College of Veterinary Medicine


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