Canis ISSN: 2398-2942

Mammary gland: neoplasia

Contributor(s): Ruthanne Chun, Isabelle Desmas-Bazelle


  • 25% of all canine tumors (50-70% of tumors in all sites in bitches).
  • Second most common tumor in bitches after skin tumors. Most common tumor in sexually intact bitches.
  • 40% malignant.
  • Benign, carcinomas, sarcomas: of interstitial connective tissue, myoepithelial cells peripheral to ducts or alveoli, ductar epithelium.
  • Cause: progestagen administration increases incidence of benign tumors and mammary hyperplasia, progestagen and estrogen increase the risk of malignant tumors; some show marked estrus-related growth.
  • Signs: various. Most dogs develop tumors in multiple glands.
  • Diagnosis: signs, histopathology.
  • Treatment: surgery if no evidence of pulmonary metastasis and/or chemotherapy if high grade of malignancy and/or metastatic disease.
  • Prognosis: favorable if complete excision, low grade, and no evidence of metastasis.
  • Prevention: ovariohysterectomy before puberty.
    Print off the owner factsheet on Breast cancer in dogs to give to your client.



  • Mammary tumors develop from benign to malignant tumors as part of a continuum influenced by hormones.
  • Mixed mammary tumor (fibroadenoma) - benign.
  • Mammary adenocarcinoma (tubular and papillary) - malignant but less so than anaplastic carcinomas.
  • Mammary sarcoma - rare.

Predisposing factors

  • Elderly dogs.
  • Hormonal - estrus cycle.
    Ovariohysterectomy prior to first estrus reduces risk of developing mammary tumor to 0.5%.
    Ovariohysterectomy prior to the second estrus reduces risk of developing mammary tumor to 8%.
    Ovariohysterectomy prior to the third estrus reduces risk of developing mammary tumor to 26%.
  • No benefit after 4 years of age.
  • Body weight: being underweight at puberty provides protection against later tumor development; obesity at young age and a diet high in red meat increases the risk of developing a mammary tumor.


  • Progestagen and estrogen administration: increases incidence of mammary tumors. Low-dose progestagen alone increases the risk for hyperplasia and benign tumors, a combination of estrogen and progestogen increases the risk of malignant tumors.
  • Possible role of BRCA gene and of HER2/erb-2 (epidermal growth factor receptor).


  • During first few estrus cycles -> small clones of preneoplastic epithelial cells established -> true neoplasms after many years.
  • Approximately 50% of malignant mammary tumors are thought to have estrogen and/or progesterone (ER + PR) receptors and some exhibit marked estrus-related growth.
  • Higher incidence (70%) of ER + PR in benign tumors and normal glands.
  • Dogs that are younger, in estrus, and intact are more likely to have receptor-positive tumors than dogs that are older, spayed, and/or in anestrus.
  • Hormone receptor expression is inversely correlated to size (large tumors), histopathology (high grade tumors), and presence of metastatic disease.


  • Usually chronic course, months-years.
  • Very malignant tumors may be more rapidly growing.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • de Araújo M R, Campos L C, Ferreira E, Cassali G D (2015) Quantitation of the regional lymph node metastatic burden and prognosis in malignant mammary tumors of dogs. JVIM 29 (5), 1360-1367 PubMed.
  • Lim H Y et al (2015) Effects of obesity and obesity-related molecules on canine mammary gland tumors. Vet Pathol 52 (6), 1045-1051 PubMed.
  • Tran C M, Moore A S, Frimberger A E (2014) Surgical treatment of mammary carcinomas in dogs with or without postoperative chemotherapy. Vet Comp Onc 14 (3), 252-262 PubMed.
  • Kristiansen V M et al (2013) Effect of ovariohysterectomy at the time of tumor removal in dogs with benign mammary tumors and hyperplastic lesions: a randomized controlled clinical trial. J VIM 27 (4), 935-942 PubMed.
  • Sorenmo K U et al (2009) Canine mammary gland tumours: a histological continuum from benign to malignant; clinical and histopathological evidence. Vet Comp Oncol (3), 162-172 PubMed.
  • Chang S C et al (2005) Prognostic factors associated with survival two years after surgery in dogs with malignant mammary tumors: 79 cases (1998-2002). JAVMA 227 (10), 1625-1629 PubMed.
  • Karayannopouloua M et al (2005) Histological grading and prognosis in dogs with mammary carcinomas: application of a human grading method. J Comp Pathol 133 (4), 246-252 PubMed.
  • Pérez Alenza D, Tabanera E, Peña L (2001) Inflammatory mammary carcinoma in dogs: 33 cases (1995-1999). JAVMA 219 (8), 1110-1114 PubMed.
  • Stockhaus C, Kohn B, Rudolph R, Brunnberg L & Giger U (1999) Correlation of hemostatic abnormalities with tumor stage and characteristics in dogs with mammary carcinoma. JSAP 40 (7), 326-331 PubMed.

Other sources of information

  • Sorenmo K U, Worley D R, Goldschmidt M H (2013) Tumors of the mammary gland. In:Small Animal Clinical OncologyEds. S J Withrow, D M Vail, R L Page. 5th ed. Philadelphia: W B Saunders. Chapter 27 pp 538-547.