Canine Soft-Tissue Sarcomas in Dogs
Canine Cancer: Diagnosis, Treatment, and Life Expectancy
You might not have heard about soft-tissue sarcomas in dogs until your vet pronounced these words. Whether your vet suspects or confirms a soft-tissue sarcoma in your dog, you will likely have many questions. A great number of pet owners aren't aware of the many conditions that dogs can develop, and vet visits often don't leave much time for questions, so it's quite common to resort to the internet to learn more.
This article is the summation of my research on this topic. You can learn a lot online as long as you rely on reputable websites, and the sources in this article will bring you to websites that you may find useful. Researching your dog's medical condition lets you know what to expect and what follow-up questions to ask at your next appointment.
What Are Soft-Tissue Sarcomas in Dogs?
You may be aware that medical terms that end in "oma" often suggest nothing good. Indeed, the word "sarcoma" comes from the following Greek words:
- sarx, meaning flesh
- oma, meaning growth
So a soft-tissue sarcoma, as its name implies, is simply a fleshy growth found in the dog's soft tissues like fat, muscle, nerves, fibrous tissues, blood vessels, and the deeper skin tissues.
Where Are They Found?
These tumors are found on connective tissues, which consist of the material that holds your dog's body structures together. As such, they can be present in any part of the dog's body.
Sarcomas account for about 15% of all the skin tumors affecting dogs, according to veterinary cancer experts. They are commonly found in middle-aged dogs as solitary masses and go ignored for a long period of time; some can grow quickly. Large dog breeds are commonly predisposed to them and male dogs appear to be more likely to get them.
Traits of Soft-Tissue Sarcomas
- Originate as pseudo-capsules
- Develop poorly defined margins
- Characterized by finger-like projections that infiltrate between muscles and layers of connective tissues
Do They Metastasize?
When you touch these growths, they may be easily movable, or more commonly, they may be fixed in place—well attached to underlying tissues as if they had roots. These tumors are generally considered minimally invasive, meaning that they are unlikely to metastasize. It is quite uncommon that they spread to the bone.
In the occasional event that they do metastasize, their preferred sites include the lungs, followed by the lymph nodes. These tumors are usually not painful but can be irritating and interfere with movement when they get large. However, just because they are minimally invasive doesn't mean they aren't serious. Soft-tissue sarcomas, when left untreated, can have a big impact on the quality of a dog's life.
Types of Soft-Tissue Cancer
Based on exactly what type of tissue the sarcoma is affecting, sarcomas are given different names. The following are some subcategories of soft-tissue sarcomas:
- Hemangiosarcoma: originating from the blood vessels
- Fibrosarcoma: originating from fibrous tissue
- Liposarcoma: originating from fat
- Lymphangiosarcoma: originating from the lymph vessels
- Leiomyosarcoma: originating from smooth muscle
- Peripheral nerve sheath tumor: originating from nervous tissue
- Rhabdomyosarcoma: originating from skeletal muscle
- Synovial Sarcoma: originating from connective tissue lining the cavities of joints and tendon sheaths
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Unfortunately, They Are Difficult to Diagnose
It's not uncommon for your vet to be unsure about your dog's diagnosis. Truth is, things can get tricky when looking for signs that confirm a sarcoma. When your vet does a fine-needle aspirate, the results may come back inconclusive, and therefore, the diagnosis may come back as non-diagnostic. This is because soft tissue sarcomas do not exfoliate well. That means they are reluctant to release cells from the mass for evaluation. Some vets will try to get a better sample by using a larger gauge needle (such as an 18 or 20 gauge).
How Are They Graded?
Sarcoma cells often appear as spindle-shaped cells with wide bodies and tapered ends. The Merck Veterinary Manual describes these "spindle-cell" sarcomas as "shaped like an octopus, with tentacles that extend deeply into the tumor bed." Yet, if the fine needle sample is inconclusive, surgical excision with biopsy is often recommended as there is more mass to evaluate.
When biopsied, the pathologist will grade the sarcoma with a grade of 1, 2, or 3, or low, intermediate, or high. Under the microscope, the pathologist looks at several factors such as the amount of dividing cells, the percentage of dying cells, and how similar the cells are to the normal ones. The grading of the sarcoma will ultimately play a big role in prognosis and treatment.
Prognosis and Treatment in Dogs
According to the National Canine Cancer Foundation, sarcomas that are more than five centimeters in diameter don't respond to chemotherapy or radiation therapy. Generally, the larger and deeper the tumor, the more likely it is to cause trouble. A rapidly growing tumor is also a much greater concern than a slowly growing one, according to the Merck Veterinary Manual.
Will My Dog Survive?
A dog's prognosis is based on several factors, keeping in consideration the grading of the sarcoma. Generally, lower-grade tumors have a better chance of being minimally invasive; whereas higher-grade tumors have a greater chance of regrowing and spreading. According to Vet Surgery Central, metastasis tends to occur at 5 to 10 percent in grade 1 tumors; up to 25 percent in grade 2 tumors; and up to 50 percent in grade 3 tumors.
Risk of Metastasis Based on Grade
Chance of Metastasis
5 to 10%
Will My Dog Need Surgery?
When these tumors are located in areas where there is ample loose skin, removal may be easy. However, often sarcomas grow in areas where skin is tight, such as the lower limbs or head. Aggressive surgery with wide margins is often needed. Complete removal may be difficult in some areas and the roots of the tumor may be left behind which leads to a recurrence.
Complications With Treatment
A lack of skin structure due to previous excision may cause the tumor to become open and difficult to remove again surgically. In other cases, tumors grow so much that the skin overlapping the tumor splits, leading to an ugly, ulcerating, open wound. When this happens, radiation therapy or even amputation of the limb may be necessary. It's a good idea to have the surgery done by a veterinary surgeon specializing in oncology. (Kim A. Selting, DVM, MS, DACVIM, oncology, offers several tips on the surgical procedure.)
How Long Will My Dog Live?
According to Robyn Elmslie, a veterinarian specializing in oncology, the average survival time in dogs diagnosed with an intermediate to low-grade soft tissue sarcoma who undergo surgery along with radiation therapy is often greater than six years. If you are looking for success rates with surgical removal, consider local tumor recurrence rates after surgery. Whether accompanied with radiation or not, these success rates tend to range from 7 to 32 percent, according to Pet Cancer Center.
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This article is accurate and true to the best of the author’s knowledge. It is not meant to substitute for diagnosis, prognosis, treatment, prescription, or formal and individualized advice from a veterinary medical professional. Animals exhibiting signs and symptoms of distress should be seen by a veterinarian immediately.
© 2014 Adrienne Farricelli