Tumors of Smooth Muscle in Cats/Dogs
Leiomyomas  (benign tumors)
Leiomyomas are benign (noncancerous) tumors that arise from smooth muscle (type of muscle found within the "walls" of
hollow organs like the bladder and abdominal cavity, the uterus, the gastrointestinal tract, the respiratory tract, the
vasculature, the skin, etc). The gastrointestinal tract is the most commonly affected but other sites where these tumors
have developed include the spleen, liver, genitourinary tract, or subcutaneous tissue (the layer of tissue directly underlying
the skin). As a result of these tumors, the pets can develop medical symptoms such as hypoglycemia (low blood sugar) or
nephrogenic diabetes insipidus.

Leiomyomas are typically small, localized and well encapsulated (enclosed). Leiomyomas of the vagina and vulva often
protrude from the vulva and are hormone-dependent. The recommended treatment for this type of tumor is

Leiomyosarcomas (malignant tumors)
Leiomyosarcomas are malignant (cancerous) tumors that can form at various anatomical sites throughout the body,
typically in older pets, and that have the potential to
metastasize (spread) to distant organs within the body. The metastatic
rate for dogs with liver leiomyosarcoma is 100% but usually drops to less than 50% for leiomyosarcomas in the intra-
abdominal sites and drops to 0% for dermal leiomyosarcomas (tumors right beneath the skin). Gastrointestinal
leiomyosarcomas commonly metastasize to regional lymph nodes and liver, but cases of metastases to the spleen and
kidneys have also been reported. The recommended course of treatment for leiomyosarcoma is a surgical removal of the
tumor. The median survival for dogs with gastrointestinal leiomyosarcoma that survived the surgery is up to 21.8 months, 8
months for dogs with spleen leiomyosarcoma and 0 months for dogs with liver leiomyosarcoma.

Does cancer cause pain in pets?
Pain is common in pets with cancer, with some tumors causing more pain than others. In addition to pain caused by the
actual tumors, pets will also experience pain associated with cancer treatments such as surgery, radiation therapy or
chemotherapy. Untreated pain decreases the pet's quality of life, and prolongs recovery from the illness, treatment or
injury. It is, therefore, essential that veterinary teams that are taking care of pets with cancer should also play a vital role in
educating pet owners about recognizing and managing pain in their pets. The best way to manage cancer pain in pets is to
prevent it, a term referred to as preemptive pain management. This strategy anticipates pain ahead of time and
administers pain medication before the pet actually experiences pain, thus ensuring the pet's maximum comfort.

To learn more about how to recognize pain in pets with cancer and what cancer pain management options are available for
your pet, please visit the
Cancer Pain Management section.

How important is nutritional support for pets with cancer?
Cancer cachexia (a term referring to progressive severe weight loss) is frequently observed in pets with cancer. Pets with
cancer lose weight partly because of lack of appetite and partly because of cancer-induced altered metabolism. Some of
the causes for decreased appetite are related to the cancer itself (for example, tumors may physically interfere with food
chewing, swallowing, and digestion process) and some may be related to the side effects of cancer treatment (for example,
some chemotherapy drugs cause nausea and vomiting, and radiation therapy can cause mouth inflammation).

Proper nutrition while undergoing cancer treatment is essential to maintain your pet's strength, improve survival times,
quality of life and maximize response to therapy. Adequate nutritional support was shown to decrease the duration of
hospitalization, reduce post-surgery complications and enhance the healing process. Additionally, pets with cancer need to
be fed diets specifically designed to provide maximum benefit and nutritional support for the patient. To learn more, please
visit the
Cancer Nutrition section.

Are there any clinical trials investigating new treatments?
There are several clinical trials ongoing for dogs with soft tissue sarcomas in pets, which are partially funded by the
institutions. To learn more about these trials, please visit the
Clinical Trials for Soft Tissue Sarcoma in Dogs section.

Additionally, there are several clinical trials available for cats and dogs with any tumor type for which your pet may qualify.
To learn more these trials (which are partially or fully funded by the institutions), please visit the
Dog Clinical Trials (any
tumor type) or Cat Clinical Trials (any tumor type) section.  

To learn more about veterinary clinical trials in general, please visit the
Pet Clinical Trials section.

  • Withrow Stephen J, and David M. Vail. Small Animal Clinical Oncology. St Louis: Saunders Elsevier, 2007.
  • Morrison Wallace B. Cancer in Dogs and Cats: Medical and Surgical Management. Baltimore: Williams&Wilkins, 1998.
© 2007 Pet Cancer Center. ALL RIGHTS RESERVED.
Last updated  2/19/2017
Comprehensive guide to cancer diagnosis and treatment in cats and dogs