Soft tissue sarcoma describes a group of cancers that arise from a dog’s connective tissues, like muscle, fat, and cartilage. These tumors are common in middle-aged or older dogs, and while any breed can be affected, some larger breeds may have a higher predisposition.
These cancers are malignant, but their behavior can vary significantly. They are often slow-growing and may not be noticed until they have reached a considerable size. A diagnosis is the first step in creating a treatment plan, as the specific type of tumor and its location will influence the recommended course of action.
Symptoms and Common Locations
The most frequent sign of a soft tissue sarcoma is a lump or mass found just beneath the skin. These masses are often firm and may feel attached to the underlying muscle or tissue. They can appear anywhere on the body, but the most common sites are the limbs, the trunk, and the head.
These tumors are characterized by slow growth, often developing over months or years. A defining feature is that they are not painful, which can lead to a delay in seeking veterinary attention. Owners may mistake the lump for a benign growth, like a fatty lump, since they can feel similar at first.
As a tumor grows, it can cause secondary symptoms depending on its location. A sarcoma on a leg might interfere with movement and lead to limping. If a tumor becomes very large, it may cause the overlying skin to stretch and break open, which can be painful. A tumor in the abdomen might result in vomiting, diarrhea, or weight loss.
The Diagnostic Process
The first step in diagnosing a potential soft tissue sarcoma is a thorough physical examination by a veterinarian. During this exam, the veterinarian will assess the size, location, and consistency of the mass. This initial evaluation helps determine the next steps in the diagnostic process.
A common preliminary test is a fine-needle aspirate (FNA). This procedure involves using a small needle to collect a sample of cells from the tumor. While an FNA can sometimes suggest a sarcoma, these tumors do not always shed cells easily, meaning the sample may not provide a clear answer.
A surgical biopsy is required for a definitive diagnosis. This involves taking a larger tissue sample from the mass for analysis by a pathologist. The biopsy confirms if the mass is cancerous and determines its “grade”—classified as low, intermediate, or high—which describes how aggressive the cancer cells appear and is a major factor in predicting the tumor’s behavior.
Once a sarcoma is confirmed, the final step is “staging” to determine if the cancer has spread, or metastasized. Staging involves tests like chest X-rays to check the lungs, a common site for metastasis, and sometimes an abdominal ultrasound. The results are important for developing a complete treatment plan.
Treatment Approaches
Surgery is the primary treatment for soft tissue sarcomas in dogs. To completely remove the tumor, surgeons perform a “wide surgical excision,” which involves removing the mass along with a significant margin of surrounding healthy tissue. Taking these wide margins, often 2 to 3 centimeters, is intended to ensure that no microscopic cancer cells are left behind.
In some situations, achieving wide, clean margins can be challenging due to the tumor’s location, such as on a limb, the face, or the chest wall. In these cases, radiation therapy is often recommended as an additional treatment. Radiation can be used after surgery to target the tumor site and eliminate any remaining cancer cells, reducing the risk of the tumor growing back.
Chemotherapy is another treatment option, but it is reserved for specific circumstances. It is most often recommended for high-grade sarcomas, as these have a greater tendency to spread to other parts of the body. Chemotherapy may also be used if staging has confirmed that the cancer has metastasized, and the decision is based on the tumor’s grade and the dog’s overall health.
Prognosis and Life After Treatment
The long-term outlook for a dog with a soft tissue sarcoma is influenced by several factors. The tumor’s grade is a significant predictor, along with its location and the success of the surgery in achieving clean margins. Dogs with low-grade tumors that are completely removed have an excellent prognosis, and surgery can often be curative.
Even for tumors that are more aggressive or cannot be completely removed, treatment can significantly extend a dog’s life. Dogs treated with surgery and/or radiation often live for 12 to 18 months or longer. The recurrence rate after surgery is estimated to be between 7% and 30%.
Life after treatment involves a period of recovery from surgery, which includes rest and careful monitoring of the incision site. Regular follow-up appointments with the veterinarian are important. These check-ups allow the vet to monitor for any signs of tumor recurrence and to ensure the dog remains healthy. Many dogs go on to live full and comfortable lives following treatment.