Skip to main navigation Skip to main content
Lesley's Place Lesley's Place

Phone: (610) 692–6272
Address: West Chester, PA

Mammary Tumors in Dogs: What to Look For

Cinderella and Sinkea

How do I know that my dog has a mammary tumor(s)?

Most dogs with mammary tumors do not exhibit any systemic signs of illness at the time of diagnosis. The tumors are confined to the areas along the mammary chain, and are easy to detect with a very simple clinical exam. Dogs do not have abundant breast tissues (unless they are nursing). Therefore, if tumors are present, they are easily palpable from the surface in the area around the nipple. In contrast to human breast cancer, we can use this method to detect even small nodules/tumors. Dogs have 4–5 pairs of mammary glands; a total of 8–10 individual glands. Dogs that are at increased risk of mammary tumors because they have not been spayed or were spayed later in life should be monitored regularly for mammary nodules/tumors. Owners of high-risk dogs should learn how to do this themselves in between the routine annual veterinary visits. Early detection and early treatment are crucial for good outcomes in dogs with mammary tumors.

Lesley’s Place works exclusively with homeless dogs diagnosed with mammary tumors. If your dog is suffering from this condition, please contact Veterinary Oncology Services and Research Center for help and resources.

Background Information

Mammary tumors are the most common tumors in older, intact female dogs, or female dogs that are spayed later in life. Here is more information about the nature and treatment of mammary tumors:

  • Mammary tumors are hormone-dependent tumors, which means removing the ovaries and the most important source of estrogen significantly decreases the risk of developing mammary tumors.
  • Mammary tumors in dogs represent a diverse group of histological subtypes and varied clinical behavior, spanning from benign to highly aggressive tumors.
  • Approximately 50% are benign, and therefore not associated with any risk of metastasis. However, if left untreated, some of these benign tumors may transform over time and become malignant. Therefore, surgical removal of all mammary tumors is recommended. Surgery also provides the tissues needed to make an accurate histopathological diagnosis.
  • Dogs often have more than one mammary tumor when they are diagnosed, and all of the individual tumors should be removed and submitted for histopathological evaluation. Carcinomas and various carcinoma subtypes represent the most common malignant group.
  • Clinicians use information about tumor type, tumor grade, tumor size, and stage when making recommendations whether additional systemic treatment is indicated, or if surgery +/- ovariohysterectomy (spay) is adequate.
  • Dr. Sorenmo’s and Dr. Durham’s recent publication on bio scoring in canine mammary tumors (see literature list)[link to publications] provides a comprehensive system to assess the risk for metastasis, and therefore the need for additional systemic therapy in dogs with mammary tumors.

See Our Publications