Tumor synonymous with neoplasm, is new abnormal growth of tissue in which cells continue to multiply in a progressive and uncontrolled manner, and which serves no useful purpose.

The term hyperplasia refers to an excessive growth of normal cells in normal tissue arrangement of an organ.

Clinical Signs

May observe any of the following:

  • The appearance of an abnormal growth that may feel soft and easily movable or firm and attached, depending on type of tumor and involvement.
  • Presence of skin ulcerations, or abscesses that do not heal with conventional treatment.
  • Changes in coordination, mobility, or vision depending on size, location, and organ involvement.
  • Changes in elimination.
  • Evidence of bleeding depending on tumor involvement and location of tumor. Sometimes can occur with prostatic tumors or uterine tumors.
  • Abnormal enlargement or distention of a portion of the body as the tumor grows.
  • Poor appetite, weight loss, and lethargy as involvement progresses.
  • Pain if present is usually seen in late stages of metastatic tumor growth.

*Note: for additional information on recognizing various signs of pain or discomfort refer to: Signs of Pain In Rats.


Tumors or neoplasms which are derived from new and active tissue growth differs from normal cell division in the following way:

Normally dividing cells are typically well defined to the tissue or organ they are specific to. They control their growth through growth factors received from other areas of the body via blood or adjacent tissue, or by reaching a point where there is no more room to grow.

In neoplasia or tumor growth the normal stimulus to stop cell growth is not there. Tissue growth is seen as uncontrolled and progressive. This type of growth is classified in many ways but one of the simpler ways is if it is either benign or malignant.

In benign tumors, growth is often slower, they remain localized and are not invasive, meaning that they do not enter adjacent tissue but push normal tissue aside. They may be encapsulated and be well demarcated (meaning it has boundary).
A benign tumor, though not invasive, will continue to grow larger. These types of growths can and do press on adjacent organs and cause difficulty with mobility and function. Because benign tumors are not invasive, many respond well to surgical intervention. If left unattended these tumors will deplete the rat’s nutrients causing weight loss and ultimate death.

In malignant growths cells are poorly differentiated, are very disorganized, and show no demarcation. These cells invade surrounding tissue and organs and obstruct normal body pathways. Metastasis develops when these cells penetrate and travel through blood or lymph seeding distant organs with similar tumors. As these types of tumors outgrow their supply of nutrients, ulceration, destruction of tissue, and necrosis (tissue death) occur. Bacterial infections can arise from the accumulation of toxic wastes because the blood supply to that area is diminished. Such rapid and metastatic growth of these cells deprives the rat of nutrients causing rapid weight loss, anemia from bleeding, and ultimately death.

Classification of tumorous growths (or cancer) are primarily based on tissue type and cell type. They can be further divided into two main groups such carcinomas or sarcomas.

Areas of cell type and tissue type include:

  • The Mesenchyme which include fibroelastic tumors and those of bone, fat, blood vessel and lymphoid tissue. They may be either benign tumors, or malignant sarcomas.

  • Those tumors with Epithelial origin may be benign or malignant carcinomas, and can be found in glandular tissue, or such organs as mammary, stomach, ureters, and skin.

  • Mixed origin tumors contain different types of cells. They are derived from the same primary germ layer, and may be either benign or malignant.

The incidence of tumorous growths in rats may depend on many different factors such as age, whether they are male or female, strain or breed, type of diet, endocrine factors and the type of environment.
They are most often seen in rats greater than 16 months.

Some types of tumors most commonly seen in rats are mammary fibroadenomas, squamous cell carcinomas (primarily seen in and around the face, jaw, Zymbal’s gland and ear), pituitary adenomas, and testicular interstitial cell adenomas. Other types observed are uterine endometrial tumors, fibrosarcomas, thyroid adenomas, and malignant lymphomas.

For further information related to specific tumor types see listing under the category Neoplasia of the Rat Health Guide.


Examples of Tumor Growth (graphic photos) and Case Histories

  • Fig. 1: Visible tumor growth
  • Fig. 2: Tumor seeding (postmortem)
  • Fig. 3: Shows male post-op tumor removal
  • Fig. 4: Case history and photo of tumor
  • Fig. 5: Fibrosarcoma of the skin, case history and photos from pre-op to post-op in male rat (Sambuca)
  • Fig. 6: Retrobulbar tumor in male rat (Voldemort)
  • Fig. 7: Chemodectoma in 23-month-old female rat (Lily). Case history, photos and audio/video of respiratory sounds. *Note: this case is as yet unverified histologically.*
  • Fig. 8: Fibroblastic tumors and incidental postmortem finding of Left Adrenal Gland Adenoma in a 31-month-old male rat (name: #7)
  • Fig. 9: Tumor removal on toe of 18-month-old male rat (Gooby). *Note: this case is as yet unverified histologically.*

Additional Example

  • Fig. 2: Zymbal’s gland tumor (from Squamous Cell CA article) in male rat (Ramekin)


Cachectic appearance.

Palpation to determine tumor presence.

Radiographic studies and ultrasonography may be useful depending on the location.

Hematology or chemistry findings may be useful.

Excision and removal of growth with histologic exam or cytology.


Surgical removal of tumors is recommended, especially while the tumor size is still small. If a tumor can not be completely excised and removed due to its location, size, or malignancy, then partial removal or debulking may provide increased comfort and mobility for the rat.

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.

  • For severe pain or first 24 hours post-op: Buprenex (buprenorphine), or Torbugesic (butorphanol).

  • For mild to moderate pain: Banamine (flunixin meglumine), Metacam (meloxicam), or carprofen. Do not use if a corticosteroid has already been prescribed.

  • *Note: for pain not controlled by the use of an NSAID (e.g., Banamine, meloxicam, or carprofen), alone, consider alternating or co-administering with a narcotic (e.g., buprenorphine or butorphanol) or narcotic-like (e.g., tramadol) medication.

Corticosteroids such as Prednisone or Prednisolone or Dexamethasone may be recommended to reduce swelling of tissue with certain types of tumors (e.g., pituitary tumors).

In the event infection accompanies the tumor broad spectrum antibiotics are the recommended drugs of choice, unless drug specificity can be determined with culture and sensitivity results.

For more information on pain medication, corticosteroids, or antibiotics, see the Rat Medication Guide.

For information pertaining to tumor tissue or type, see individual listing of tumors/neoplasms.

Euthanasia should be considered 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 felt, soft t-shirt type material or ink-free paper towels. Avoid using material such as terry cloth type towels that can ravel. Also avoid litter-type bedding, post-op, until healed to prevent the chance of wound contamination or infection.
  • Provide additional warmth to maintain body temperature within normal limits. It is essential that the rat does not become overheated or dehydrated. The rat should also be able to move away from the heat source if it becomes uncomfortable. If the rat is unconscious or immobile extreme care must be taken to keep the heat low and stable.
    • You can use an isothermic product that is heated in the microwave such as SnuggleSafe┬«. Make sure to follow the product directions carefully and wrap in a towel before placing in the cage. SnuggleSafe┬« will provide heat for 12 hours before needing to be reheated. Other similar types of product may vary in re-heat time. Check directions for individual product.
    • If using a heating pad (good for long term use) use only the low heat setting, put a thick towel in between the pad and the cage bottom, and place beneath a corner of the cage.
    • If none of these options are available you can use a plastic bottle filled with hot water, and wrapped in a towel, in the corner of the cage.
  • Medicate for post-op pain as needed.
  • Body wrap may be required if thread sutures are used.
  • In the event of dried or excess drainage, the incision site may be cleaned with a moistened Q-tip (swab), using warm water or normal saline.
  • Assess nutritional status:
    • For 24 to 48 hrs post-op, feed iron-rich foods to prevent anemia (cooked liver, scrambled or hard-boiled
    • Provide additional nutritional supplement, such as Soy baby formula, Ensure, Boost, NutriCal paste (for dogs and cats found in pet store), mashed avocado, and baby foods during recuperation. Include multi-vitamin supplement (can be found in pet store) if food intake is poor.
    • Encourage fluid intake while recuperating, such as water, Jell-O 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 thawed as needed.
      *Note: a juicy type of fruit also provides an additional fluid source in the diet.
  • Contact veterinarian if any of the following are observed: swelling, redness, or pain at the incision site, or if there are signs of increased weight loss, lethargy, or changes in habits.


  • Increased comfort and mobility.
  • Increased quality of life.
  • Post-op pain is relieved.
  • Incision site is free from infection.
  • Emotional support for those having to consider euthanasia for their rat.


  • A low fat, low calorie diet that includes fresh fruits and vegetables (e.g., broccoli).
  • Maintain healthy weight and prevent obesity from over feeding, or feeding too many treats.
  • Discuss, with veterinarian, the benefits vs risks of spaying.
  • Routinely doing a physical assessment by palpation of your rat at home for early detection. Doing this even at an early age will give you an awareness of what is normal for your rat.
  • Early detection of the tumor while the growth is still small decreases operative time, enhances recovery period, and improves outcome.


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