Benign Mammary Fibroadenoma

The most common tumor of rats is the benign mammary fibroadenoma. Because rats have extensive mammary tissue, subcutaneous tumors may be found anywhere on the body. Tumors can occur in either females or males. Clinically, the tumors appear as subcutaneous lumps and can grow quite large, eventually ulcerating or interfering with eating and drinking or locomotion. Benign mammary tumors are usually encapsulated and prognosis improves with surgical removal. Recurrence in another location is frequent, but progression to malignancy is rare. 1

Clinical Signs

  • Typically seen as a soft, circumscribed (round), or somewhat flat appearing growth that can be movable on palpation, to a more firm and attached growth (seen more in malignancy) anywhere along the region of mammary tissue.
  • Impaired mobility as the growth becomes larger.
  • Ulceration and necrosis of tissue in later stages.
  • Increased appetite with no weight gain as dietary intake is redirected to tumor growth.
  • Poor appetite, weight loss, and lethargy as involvement progresses.
  • Development of one or more growths along mammary chain.

Excision and removal of tumor is recommended. Note: preanaesthetic fasting of rats is not necessary since vomiting does not occur in this species. Free access to both food and water should be provided until just prior to anesthesia (Flecknell, 1991).

Pre or post-op prophylactic broad-spectrum antimicrobials may be indicated in elderly, debilitated or immunocompromised rats.

Rats do experience pain with surgical procedures. The type of pain medication used post-op should be determined based on extent of procedure and the anticipated severity of pain. 2


  1. Merck Veterinary Manual
  2. Health Guide: Mammary Tumor

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