Definition
Mammary fibroadenoma: This type of growth is a fibrous, benign, epithelial tumor in which cells are derived from glandular tissue.
Mammary adenocarcinomas: A malignant growth in glandular organs and arising from epithelium.
Clinical Signs
Typically seen as 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.
May see poor appetite, weight loss, and lethargy as involvement progresses.
Etiology
Mammary tissue is extensive in rats and is found ventral, lateral and dorsal, running from the shoulder and chin area to the base of the tail. Tumors can arise anywhere that this tissue type is present, but is most often seen at the pit of the arm, abdomen, and groin of female rats greater than 18 months of age. These tumors may also present in males, though are not as numerous.
The most common mammary tumor found in rats is that of the mammary fibroadenoma, a benign encapsulated tumor. Rats do well when having these tumors removed, especially since the tumor tends to remain localized and is less invasive. Though these tumors can be successfully removed, due to the extent of mammary tissue in the rat, they do tend to reoccur.
Mammary tumors that are allowed to continue growing without treatment can become quite large, encompassing up to half the body weight of the rat. These tumors just by virtue of how large they can grow, will not only impinge on other organs, but inhibit the rats mobility, and result in difficulty grooming and being able to feed itself. Weight loss occurs as the tumors growth deprives other tissues and organs of needed nutrients.
Mammary adenocarcinomas, are felt as a firmer more attached tumor, and are less often seen than the fibroadenomas. They not only invade surrounding organs, but can metastasize by traveling through lymph and blood vessels to lungs and bone, and can result in seeding in other areas of the body.
Although most mammary tumors in rats are benign, they will continue to grow larger, and if not removed will eventually ulcerate and bleed causing anemia. As the tumor becomes necrotic, it can release toxins into the blood, which can lead to toxemia, and septicemia, and ultimately result in organ failure, and death.
Early removal of the tumor, even if malignant, can often extend the rat’s life. Even debulking a tumor, if not able to remove due to its involvement, will afford the rat more comfort and improve mobility.
Photo examples of mammary tumors have been provided in the following figures:
- Fig. 1: Palpation of tumor.
- Fig. 2: Pooka’s post-op incision site.
- Fig. 3: Large mammary tumor (note: contains post mortem and necropsy photos, very graphic).
Diagnostics
Palpation of ovoid, discoid, or varied shaped mass. May be well demarcated.
Large mass may show ulceration or necrosis.
Rat may appear cachectic as tumor continues to grow.
Magnetic Resonance Imaging (MRI) may be useful with soft tissue tumors.
Histologic examination of tissue.
Treatment
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.
The following is recommended for pain control with post-op procedures:
For severe pain or first 24 hours post-op -Butorphanol or
Buprenorphine.
For milder form of pain control in the post recovery period:
Banamine (flunixin meglumine)
or
Tylenol
(acetaminophen)
For information on above listed medications, refer to the Rat Medication Guide.
Additional Considerations
Discuss with vet the possibility of spaying in female rats if general health status is good.
Tamoxifen for estrogen stimulated tumors may be a treatment of choice in elderly rats with additional high risk health problems, or where surgery is no longer an option.
Refer to the Rat Medication Guide for information regarding Tamoxifen
Possible euthanasia if tumor affects quality of life after treatment has been tried.
Nursing Care
Provide hospital cage during recovery, or if there are concerns that their cage mates may groom sutures or wound site.
Provide clean bedding daily such as cloths or ink-free paper towels. Avoid litter-type bedding post-op, and until healed, to prevent the chance of wound contamination or infection.
Provide additional warmth using a hot water bottle or heating pad on low heat under one half of cage (ensure rat does not overheat and become dehydrated) post-op.
Medicate for post-op pain as needed.
Body wrap may be required if thread sutures are used.
Should there be dried or excess drainage, the incision site may be cleaned with a moistened Q-tip (swab), using warm water or normal saline.
Contact vet if any of the following are observed: swelling, inflammation (redness) or pain at the incision site, or signs of increased weight loss, lethargy, or changes in habits.
For 24-48 hrs post-op, feed iron-rich foods to
prevent anemia (cooked liver, scrambled or hard-boiled
eggs).
Provide additional high calorie foods or food supplements such as Nutri-Cal Paste, canned Ensure, Soy or soy formula, during recuperation. Include additional multi-vitamin supplement (can be found in pet store) if food intake is poor.
Encourage fluid intake while recuperating, such as water, Jello water, or electrolyte replacement drinks such as Pedialyte or Gatorade which can be found in local grocery stores. Please note that Pedialyte is only good refrigerated for 24 hours after opened, but can be frozen as ice cubes and kept longer, and then thawed when needed.
*Note: a juicy type of fruit also provides an additional fluid source in the diet.
Outcomes
Medication regimen for Tamoxifen if appropriate.
Post-op pain relieved.
Incision site free from infection.
Increased comfort, mobility and quality of life.
Weight loss prevented.
Emotional support for those having to consider euthanasia for their rat.
Prevention
Offering a diet that is nutritiously low in fat, calories, amines and nitrates, is recommended.
Spaying may be recommended for prevention.
Early detection of the tumor while the growth is still small decreases operative time, enhances recovery period, and improves outcome.
Posted on July 5, 2003, 10:25,
Last updated on April 12, 2008, 20:09
| Neoplasia | Reproductive
