Soft Tissue Sarcomas In Dogs

In dogs and cats, soft tissue sarcomas (STS) are a general class of tumors involving those coming from the connective, muscle, or nerve tissues. Cancers like soft tissue sarcoma arise from the abnormal, uncontrolled production of these cells. These tumors can develop on the chest, back, side, legs, and facial tissues of your pet, since connective, muscle, and nervous tissues are present throughout the entire body. Estimates suggest that soft tissue sarcomas make up approximately 15% of skin cancers in dogs and 7% in cats. One type of STS commonly found in dogs is fibrosarcomas.

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What are the Various Types of Soft Tissue Sarcomas in Dogs?

There are various types of sarcomas in dogs that can develop on or around the soft tissues. While identifying the type of canine sarcoma is valuable, when it comes to soft tissue sarcomas, it is more important for you and your veterinarian to monitor the size and growth of the mass. The rate of growth of the sarcoma can have an impact on its ability to metastasize — or spread — throughout your pet’s body. Dogs are at risk of developing canine soft tissue sarcoma around the time they reach the age of 10, though it can be seen at any age. It’s worth noting that there is no specific breed that is more at risk of developing these tumors, nor is a particular sex at a higher risk.

Some types of sarcomas include:

• Fibrosarcomas
• Nerve sheath tumors
• Schwannomas
• Hemangiopericytomas

Liposarcomas and rhabdomyosarcomas are more aggressive forms of sarcomas. Approximately 10-20% of soft tissue sarcomas will metastasize and spread throughout the body. In most cases, when this tumor does metastasize, it spreads to your dog’s lungs or lymph nodes.

What are the Clinical Signs and Symptoms of Soft Tissue Sarcoma in Dogs?

The clinical signs of sarcomas are not always obvious and are most often discovered during a routine veterinary exam. The following are a few clinical signs that you can look for at home to ensure that your pet gets the treatment he or she needs as soon as possible:

• Visible mass or lump under the skin
• Pain, tenderness, or discomfort near the tumor
• Limping, lameness, or difficulty moving
• Swelling in the affected area
• Fatigue, weight loss, or changes in behavior (in advanced cases)

These general warning signs can be further supported by more specific details, such as:

• Mass: The most common symptom of a soft tissue sarcoma is a mass that has formed near the soft tissues and underneath the skin. The lump or bump can vary in size, so it may not necessarily be visible to the naked eye. You may notice a mass as you are bathing your pet, brushing your dog’s coat or simply cuddling with him or her. Your veterinarian may also discover a mass during a routine exam. For most dogs, the soft tissue sarcomas are not painful.
• Limping or Lameness: In some cases, if the soft tissue sarcoma develops underneath the dog’s legs, then the growth and development of the mass could cause your dog to limp or have difficulty walking. Again, the sarcoma itself is likely not painful, but the size of the tumor may prevent your dog from being able to walk normally.

How are Soft Tissue Sarcomas In Dogs Diagnosed & Staged?

If you or your veterinarian discovers a soft tissue sarcoma on your dog, there are several steps that need to be taken. Your vet will likely start the diagnostic process by running routine blood work on your dog. Your vet may take three-view chest X-rays to see if the tumor has spread to the lungs. An important step is typically to aspirate — or withdraw cells— from the mass to verify that it is in fact a soft tissue sarcoma. Finally, the mass may undergo surgical biopsy to identify which type of soft tissue sarcoma it is.

What are the Treatment Options for Soft Tissue Sarcoma in Dogs?

Once the veterinarian has completed the diagnostic screening, you should have a better understanding of your pet’s treatment options. If the tumor has not metastasized, these are the treatment options that may be available for your dog:

• Surgery: Complete removal of the tumor with a wide margin of healthy tissue is typically the most effective treatment for soft tissue sarcoma. When 3 cm margins are achieved, surgery alone can cure the cancer in 90% of cases. Incomplete margins increase the likelihood of recurrence within 6–12 months.
• Chemotherapy: If a tumor cannot fully be removed with surgery, chemotherapy can be used to help slow the tumor’s growth and development. Chemotherapy is not a cure but rather a way to prolong the life of your dog.
• Stereotactic Radiation: Stereotactic Radiation is one of the most innovative treatment options available for dogs with soft tissue sarcoma. At PetCure Oncology, our team is qualified to provide this treatment option, which is designed to maximize damage to the tumor without harming the other tissues and organs in the surrounding area. Stereotactic radiation can be administered in fewer treatments and has fewer side effects than chemotherapy. SRS is a form of radiation therapy in which a patient may only need 1-3 radiation treatments, minimizing side effects. This novel form of RT is showing much promise for treatment of these tumors
• Conventional Fractionated Radiation Therapy (CFRT) is a form of RT using a lower dose per treatment than SRS.  As such, a patient may need 19-21 treatments. CFRT can cure 76% of incompletely resected soft tissue sarcomas.  

How Radiation Therapy Helps Treat Soft Tissue Sarcoma in Dogs

Radiation therapy can play a vital role in managing soft tissue sarcoma, especially when surgical margins are incomplete or when tumors are inoperable due to their location. Two of the main forms of radiation therapy that are available and widely used include:

• Conventional Fractionated Radiation Therapy (CFRT): Administered over 19–21 sessions, CFRT uses lower doses of radiation per session. It is effective in reducing tumor size and, according to a published study by McEntee et al. (Veterinary Radiology & Ultrasound, 2000), can cure 76% of incompletely resected sarcomas when combined with surgery.
• Stereotactic Radiation Therapy (SRS/SRT): SRS/SRT is a highly targeted approach to radiation therapy that delivers high-dose radiation to a tumor in just 1–3 sessions. A few of the advantages of this novel approach are that it minimizes damage to surrounding healthy tissues, offers a shorter treatment timeline, and is well-tolerated by most patients. SRS/SRT is especially beneficial for dogs with residual cancer after surgery or for those dogs who are not surgical candidates.

2023 Study Featured in JAVMA

PetCure Oncology was published in JAVMA in the July 2023 edition, highlighting the benefit of using a liquid fiducial marker post-surgery to help target SRS/SRT. These liquid fiducial markers allow stereotactic radiation (SRS/SRT) to be delivered safely and effectively to cancer patients who have undergone surgery to remove a tumor but are still found to have residual cancer. This advancement was tested through a PetCure clinical trial conducted between May 2017 and March 2019 with findings published in the July 2023 edition of JAVMA, providing new hope for many dogs and cats that are in need of additional cancer care after undergoing tumor-removal surgery. This cutting-edge technology allows for the insertion of a liquid fiducial marker at the tumor site, either during or after surgery, providing a necessary target for radiation therapy treatment planning. This innovative approach offers new hope for our furry companions in their fight against cancers like soft tissue sarcoma, mast cell tumors and adenocarcinoma like those found in anal sac adenocarcinoma.

What is the Prognosis for Dogs Diagnosed With Soft Tissue Sarcoma?

When soft tissue sarcomas in dogs are treated with surgery, chemotherapy or stereotactic radiation, the pet’s life expectancy is often prolonged and the prognosis is favorable. However, if the tumor has metastasized, then the cancer is likely terminal. The amount of time that your dog has left will depend on the type of sarcoma that has developed and its rate of growth.

Common Questions About Soft Tissue Sarcoma in Dogs

How long will my dog live with soft tissue sarcoma?

Prognosis depends on tumor grade, size, and treatment. Dogs treated with surgery and/or radiation often live 12–18 months or longer, especially if clean margins are achieved. Without treatment, survival may be limited to a few weeks to months due to tumor progression or metastasis. (Source: Vail et al., Withrow & MacEwen’s Small Animal Clinical Oncology, 6th ed.)

How aggressive is soft tissue sarcoma in dogs?

These tumors vary by grade. Most are low to intermediate grade, meaning they grow slowly and have a low risk of spreading. However, high-grade sarcomas can grow quickly and metastasize in 20–25% of cases, often to the lungs or lymph nodes¹.

When to euthanize a dog with soft tissue sarcoma?

Pet owners may consider euthanasia if their dog experiences significant pain, mobility loss, poor response to treatment, or reduced quality of life. Consulting with your veterinary oncologist can help guide this decision based on your pet’s comfort and disease progression.

What are the first signs of soft tissue sarcoma?

Often detected as a firm, non-painful lump under the skin, sarcomas may grow slowly over weeks or months. Dogs may show no other signs until the mass interferes with movement or function. Routine physical exams are key to early detection².

Find a PetCure Oncology Location Near You

If your dog has been diagnosed with soft tissue sarcoma, it’s important to know that you have options. Your dog deserves the best possible care, and the experts at PetCure Oncology can provide all the treatment options that your beloved pet requires. We believe that dogs deserve the same sort of care and respect as human patients, and we specialize in providing this unique form of support. For more information about PetCure Oncology and our innovative treatment options, find a location near you today.

Reviewed by Neal Mauldin, DVM, DACVIM (Internal Medicine and Oncology), DACVR (Radiation Oncology)

RELATED: Pet Hero: Brownie the Labrador Retriever Mix, Pet Hero: Cancer Didn’t Stop Kita The Adventurous Pup, Soft Tissue Sarcomas In Cats, Case Study: Maxillary Sarcoma, NIH: Single high-dose radiation therapy and liquid fiducial markers can be used in dogs with incompletely resected soft tissue sarcomas

Additional references: 1 NC State Veterinary Hospital, 2 Merck Vet Manual