What is a soft tissue sarcoma? If you’ve ever asked yourself this question or you’d like to know more about this type of tumor, you’re in the right place. In this article, we’ll look at its definition, how it is diagnosed, the treatment for soft tissue sarcoma in dogs, as well as its prognosis.
What is an STS?
Soft tissue sarcoma is a generic name utilized for several types of cancers which affect an array of tissues. Under this umbrella group, there are tumors that arise both from the subcutaneous connective tissue and the skin per se. The cancer can affect the fat (liposarcoma), the nerves (Schwannoma, neurofibrosarcoma, malignant peripheral nerve sheath tumor), the fibrous connective tissue (fibrosarcoma), or the so-called ‘pericytes’ of small blood vessels beneath the skin (hemangiopericytoma).
Some types are more aggressive than others — histiocytic sarcoma, rhabdomyosarcoma, and hemangiosarcoma) — and these aren’t usually included in the denomination of soft tissue sarcomas especially because they are to be considered separately. However, those that we have mentioned before have many similitudes in terms of their behavior.
They can appear at any anatomic site, they are discrete and encapsulated, but they are quite invasive. It’s more or less common for a tumor to regrow in the same spot where surgical removal was performed.
As is the case with other types of cancers, STS can be categorized as low grade soft tissue sarcoma in dogs, but it can also be intermediate and high grade. The vast majority of those that are diagnosed in veterinary practices are low to intermediate grade. As such, they have a low chance of ever spreading to other areas in the body such as other organs (the lungs included). On the other hand, high-grade sarcomas have an approximate 25 to 40% potential of metastasis.
What Causes Soft Tissue Sarcoma in Dogs?
Unfortunately, much like other types of cancer, soft tissue sarcomas do not have a particular cause, and as such, they can’t be prevented effectively by pet parents. They are somewhat more common in middle-aged to old dogs, and they have been found to affect larger breeds to a higher extent compared to others.
The location of the tumor is what determines the clinical signs. As we have noted in the beginning, this type of tumor can occur pretty much anywhere in the body where there is conjunctive tissue, for example, so masses can develop on the body surface or inside various organs (from the kidneys to the heart). They are known to grow slowly, so the symptoms become more severe as they become larger.
What’s worse about those that affect the internal organs is that they cause almost no clinical manifestation until they are quite large. Given that the location of the sarcoma causes its signs, you might notice halitosis in a dog that has tumors in his or her mouth, as well as difficulty eating or swallowing. Sometimes, epistaxis (bleeding from the nose) can be present, as well. Dogs that have sarcomas in their digestive tract can experience diarrhea or vomiting.
Microscopic examination using a tissue sample (such as one extracted via biopsy) can assist the vet in making a definitive diagnosis of a soft tissue sarcoma.
X-rays, an MRI, or a CT scan can be useful, as well, especially when it comes to determining the nature of the tumor and its extent, which can be extremely helpful for the medical professional when it comes to choosing the correct treatment and surgical approach. Cell samples are utilized to identify the exact type of soft tissue cells that form the mass.
In general, cancer can be treated using one or several types of treatments, but there are mainly three kinds available depending on the tumor type — surgery, chemotherapy, and radiation therapy.
Surgical excision must be deep, as well as wide, so as to remove all of the tumor tissue. If the surgical treatment was performed correctly and all of the margins of the cancer were removed, there might be no further treatment needed.
On the other hand, if the mass was not removed with adequate margins, the pathologist might have to re-assess the mass under the microscope and a second operation might be required. In some situations, your vet might recommend the surgical treatment even if there is little to no chance of removing the entire tumor. In such a situation, the specialist takes several factors into account and they range from your dog’s age and general health status to the grade of the tumor, its size, as well as its location and rate of growth.
Chemotherapy can be recommended for high-grade sarcomas because these medications either delay the onset of metastases or prevent them altogether. Most dogs tolerate chemotherapy quite well, especially when compared to cats, and many vets recommend combined therapies (surgery and chemotherapy, for example) for the best type of recovery.
Radiation therapy is another option, especially in cases where aggressive surgery is not possible without the loss of function of an organ or without jeopardizing the life of the animal. Even though it is mostly well tolerated, it can be somewhat more painful compared to the other treatment choices and it does have several side effects at the site where it is performed.
On the other hand, it is extremely helpful when it comes to ‘neutralizing’ tumors, especially small ones as with them, radiation therapy can stop or delay the risk of metastases. It does not have the same effect on large tumors, unfortunately, as there were many cases where they regressed and eventually had to be removed surgically anyway.
The pet’s life expectancy largely depends on the location and nature of the tumor, as well as the exact time it was diagnosed. However, it is generally considered that dogs that receive surgical treatment will live for approximately four years following the operation while those that undergo both surgery and radiation therapy can live up to six years following the treatment.
The metastatic rate of most soft tissue sarcomas is up to 20%, and compared to other types of cancers, that is a low figure.
Dogs that have already developed metastases by the time they are diagnosed have a poor prognosis, and so do those that have sarcomas in their abdomen, no matter the organ that was affected. Generally, most such tumors have a high likelihood of being metastatic. The pets that have sarcomas in their mouth can also get a poor prognosis given the difficulty to treat the tumors surgically or using radiation.
Soft tissue sarcomas that are found in the skin or in the limbs of dogs can be treated more easily compared to others, so the prognosis can be good but it also has to take into account factors such as the dog’s age and general health.