Mammary tumors are very common in rats and a most commonly seen in rats over 1 year of cage. They can be seen in both male and female rats but are more common in females. They can appear nearly anywhere on the torso due to the extensive amount of mammary tissue in this species. Benign fibroadenomas are the most common. Cancerous adenocarcinomas represent less than 15% of mammary tumors in rats. Many mammary tumors are hormonally responsive in rats and can occur secondary to prolactin hormone-secreting tumors in the pituitary gland within the brain.
The primary symptom is the presence of any subcutaneous mass occurring anywhere from the neck to the groin region
Abscesses and mastitis (mammary gland infection) can appear similar to mammary tumors in rats.
Your vet may recommend a fine needle aspirate of the mass, full body radiographs to look for evidence of spread throughout the body, a complete blood count, and a serum biochemistry panel before surgical removal. Following the mass should be sent off for testing to determine whether or not it is cancerous.
Spaying a rat decreases the incidence of mammary tumors significantly. Spaying a rat prior to 7 months of age can decrease the incidence as much a 75%.
Surgery to remove the mass is the treatment of choice. If possible, spaying should be done at the same time to decrease the chance of new tumors developing. In patients where spaying is not an option, a hormonal implant can be used to help decrease tumor recurrence. Cabergoline may be prescribed to patients where mammary tumor development occurred secondary to prolactin-secreting pituitary tumors. Tamoxifen can be used in estrogen-responsive mammary tumors, but this expensive treatment if only effective against adenocarcinomas (<15% of tumors), and misuse can result in the development of liver tumors. Antibiotics or pain medications may be prescribed if the tumors has developed any wounds or sores. Pain medications should be provided following surgery.
Recurrence is common in uninvolved mammary tissue and repeat surgeries often required. Metastasis (spread of tumor to other organs) does not occur with fibroadenoma, so the overall prognosis with this type of tumor is fair. Death may occur due to enlarged tumors that ulcerate and become secondarily infected or cause excessive blood loss.
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