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Mammary Tumors

Mammary tumors are the most common form of cancer in intact female dogs. Igenity Canine Wellness testing detects genetic variants for higher risk of mammary cancer that were identified in English Springer Spaniels. Research has been done in other breeds to identify candidate genes for future research and it’s likely that more study will unravel the genetic contribution of this common, but complicated disease.

As with many cancers, mammary carcinomas affect dogs and people. It’s estimated that the incidence of mammary tumors in intact female dogs is about 3 times higher than in human women.1 Due to the similarities in cell type and prognostic indicators of canine mammary carcinoma and human breast cancer, both species will benefit from research into new tools in prevention and treatment.

Genotype Phenotype
No variant detected No increased risk based on the variant tested
One or more variants detected Patient could be at increased risk for mammary carcinoma

Early Spay dramatically decreases risk for mammary cancer

Mammary tumors are a common cancer in female dogs. Early detection is key to treatment success. Spaying young dogs decreases risk of mammary tumors.


English Springer Spaniel

Initial study included nearly 500 dogs from Sweden, Norway and the United Kingdom. The effects of these risk variants have not been validated in other breeds.


Mammary cancer symptoms:

  • Palpable lump or lumps under the skin on the abdomen
  • Ulceration of the skin over the mammary glands
  • Painful breasts
  • Red (blood) or yellow (pus) discharge from nipple
  • Generalized weakness, lethargy or poor appetite


Risk can be significantly decreased by early ovariohysterectomy (spaying.) Spaying prior to the second heat cycle may be recommended in at-risk dogs not intended for breeding. The risk of mammary cancer is substantially lower for dogs spayed before 2 years of age.

Risk of mammary cancer (not accounting for increased genetic risk).3

Age of Spay Surgery Risk of Mammary Cancer
Prior to first heat cycle 0.5%
Prior to second heat cycle 8%
After the second heat cycle 26%

According to the American College of Veterinary Surgeons, spaying female dogs at the time of tumor removal is unlikely to decrease the chances of metastasis or future tumor development. However, this can prevent other diseases such as pyometra (uterine infection). Spaying is more effective at cancer prevention when pets are young.


One study has shown a relationship between obesity at 1 year of age and 1 year prior to diagnosis within a group of dogs with mammary tumors compared to healthy dogs. Other risk factors identified included feeding homemade rather than commercial diets and high intake of beef and pork and low intake of chicken4.


This genetic test evaluates 8 specific DNA markers within 3 chromosomal locations shown to predispose to mammary cancer. Two risk variants detected by this genetic test were initially discovered in a group of English Springer Spaniels from Sweden. Risk variants are not well studied in other breeds or regions. Genetics is a factor in development of mammary cancer, likely due to many different genes and DNA loci.


Other genes and risk loci have been implicated in the development of mammary carcinoma and are not included in this test. This set of risk markers has not been evaluated in breeds other than the English Springer Spaniel.


  1. (2018). Overview of Mammary Tumors. Retrieved from: https://www.merckvetmanual.com/reproductive-system/mammary-tumors/overview-of-mammary-tumors
  2. Melin, M., Rivera, P., Arendt, M., Elvers, I., Murén, E., Gustafson, U., Starkey, M., Borge, K.S., Lingaas, F., Häggström, J., Saellström, S., Rönnberg, H., Lindblad-Toh, K. (2016). Genome-Wide Analysis Identifies Germ-Line Risk Factors Associated with Canine Mammary Tumours. PLoS Genetics, 12(5). https://doi.org/10.1371/journal.pgen.1006029
  3. American College of Veterinary Surgeons. (2018). Mammary Tumors. Retrieved from: https://www.acvs.org/small-animal/mammary-tumors
  4. Alenza, D. P., Rutteman, G. R., Peña, L., Beynen, A. C., & Cuesta, P. (1998). Relation between Habitual Diet and Canine Mammary Tumors in a Case-Control Study. Journal of Veterinary Internal Medicine, 12(3), 132–139. https://doi.org/10.1111/j.1939-1676.1998.tb02108.