Common Canine Cancers: What You Need to Know About Soft Tissue Sarcomas in Dogs

By Robyn Elmslie; DVM, DACVIM (Oncology)- Veterinary Referral Center of Colorado (VRCC)

Soft tissue sarcomas are one of the most common cancers to affect dogs. These tumors typically grow in the skin or in the subcutaneous tissues under the skin. Thus, pet owners usually find these tumors as skin lumps or masses while they are petting their dogs. Soft tissue sarcomas arise from connective tissue, which is a tissue that essentially holds the skin and other organs together and provides a structural framework for the body. As the tumors grow, they form a root system—similar to a weed in a garden—which invades deeply into the surrounding normal tissues. This deep invasion of the root system makes these cancers very challenging to treat or cure. 

Signs and Symptoms

The development of a mass lump on the skin or just under the skin is the most common sign of soft tissue sarcomas in dogs. The mass may be moveable in some cases, and in other cases, the tumor will be fixed in place, adhered to the underlying tissue. Depending on the location, the tumor may be painful, but for the most part, the mass does not bother the patient until it is very large.

Treatment Options

If the soft tissue sarcoma grows on a part of the body with ample loose skin around the tumor and body fat underneath it, then surgical removal of the tumor is the most common form of treatment. Your family veterinarian or veterinary surgeon can often successfully remove enough surrounding tissue to completely excise the microscopic root system of the soft tissue sarcoma, thereby ensuring complete removal and cure. However, all too often the tumors grow in a location of the body where there is not ample loose skin or body fat, such as on the lower limbs or on the head and neck. In these locations, it is very difficult for the veterinarian to completely remove the tumor’s microscopic roots. While it may appear to the naked eye that the tumor has been fully removed, if tumor cells from the roots of the mass have been left behind, they will continue to invade deeper into the normal tissues and eventually form a new tumor mass. Since there is often less loose skin than there was prior to the first surgery, this can cause the new tumor to stretch (and ultimately grow through) the skin and create an open, ulcerated wound. The open wound, which can no longer be completely removed surgically, ultimately impacts the pet’s quality of life, and can lead to amputation of the limb or even euthanasia.

In situations where it is not possible to completely excise the tumor surgically, then radiation therapy is an excellent option to prevent regrowth of the tumor. Radiation therapy is a beam of energy applied directly to the surgery scar and surrounding tissues to kill all microscopic tumor cells that have been left behind after surgery. Since radiation therapy does not affect any tissue outside the treated area, your pet will not experience side effects to other organs. The average survival time for pets with an intermediate to low-grade soft tissue sarcomas that undergo radiation therapy is often greater than six years. Therefore, the use of radiation therapy in combination with surgery is a highly effective treatment option that can allow your pet to live out their normal lifespan, in many cases, with manageable short-term side effects.

For more information about our oncology team, our patients and other oncology topics, please visit, tissue or