Download Canine Soft Tissue Sarcomas

www.southpaws.com
SouthPaws Oncology Service
8500 Arlington Boulevard
Fairfax, Virginia 22031
Tel: 703.752.9100
Fax: 703.752.9200
These tumors are cancers of connective tissue. They include fibrosarcomas,
chondrosarcomas, myxosarcomas, undifferentiated sarcomas, liposarcomas, malignant
fibrous histiocytomas, hemangiopericytomas, peripheral nerve sheath tumors,
rhabdomyosarcomas, leiomyosarcomas, neurofibrosarcomas, and several others. This
class of cancers can be talked of as a group as their behavior is quite similar. This group
DOES NOT include hemangiosarcoma, osteosarcoma, synovial cell sarcoma, and
histiocytic sarcomas as these cancers have different and unique behavior patterns for
each type of cancer.
Soft tissue sarcomas (STSa) in dogs are locally invasive cancers. They are never
confined by a “capsule”. They can originate in any portion of the body (skin, subcutis,
muscle of the head, neck, trunk, flanks, legs, hips, etc.) as well as within body cavities
and internal organs.
The behavior of a STSa can be predicted based upon two factors: grade and margins of
surgical excision. In order to determine grade, a large section biopsy (incisional or
excisional) must be performed. Low/intermediate grade STSa have between a 10 and
20% chance of metastasizing from the primary tumor site to the lungs (predominantly).
High grade STSa have a 50-70% chance of metastasis.
Surgical excision of STSa tends to be the primary form of therapy. Careful planning
(sometimes requiring advanced imaging) before surgery gives us the best chance of
removing the entire STSa. Two centimeter margins in an en bloc excision pattern is the
usual goal for the surgeon. This approach means that the surgeon’s blade is an inch
away from the known edge of the tumor. This incision is deepened to include underlying
muscle, or other tough connective tissues, below the known deep extent of the tumor to
remove a block of tissue surrounding the STSa. The surgeon attempting a local cure on
this type of cancer should never “shell out” this type of tumor, or cut it out with narrow
margins, then go back and try to take more tissue during the same procedure. Margins
of this “block” of normal tissue surrounding the cancer are inked, and the entire block
submitted for histopathology. The pathologist then examines cut sections and tells us
whether the margins are clear of cancer cells and by what distance. If a true “clean
margin” has been obtained, the chance of local recurrence is less than 5%.
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www.southpaws.com
SouthPaws Oncology Service
8500 Arlington Boulevard
Fairfax, Virginia 22031
Tel: 703.752.9100
Fax: 703.752.9200
continued
If a “clean margin” and low/intermediate grade STSa has been diagnosed (post-surgical
excision), then no additional local or systemic therapy may be necessary as the chance
for local recurrence is under 5%, and the chance for systemic metastatic disease is
under 20%.
If a low/intermediate grade STSa has been diagnosed, but margins were NOT clean, we
have the following treatment options:
1. Repeat surgery with wider margins if still possible while treating the entire scar as
tumor for purposes of resection.
2. Full course radiation therapy to the incision to include these newer wider margins.
This treatment has an 80% chance of preventing local recurrence.
3. Watchful waiting – just as soon as any evidence of local recurrence happens, we get
aggressive surgically at that time, assuming overall state of health and repeat staging
testing shows no evidence of spreading cancer.
4. Metronomic therapy to try to slow the chance of local recurrence.
5. Intralesional chemotherapy to the incision site within 1-2 months of surgery MAY
slow or prevent local recurrence.
If a high grade STSa has been diagnosed, systemic chemotherapy is often used after
surgery to try to maximize quality and quantity of life. Remember, since 50-70% of these
tumors metastasize to the lungs or other organs, it is rare for dogs with this type of STSa
to live for more than 6-8 months without successful chemotherapy. Doxorubicin-based
chemotherapy protocols are the most commonly used and have good response rates
(most responding dogs do not develop metastatic disease for 1-2 years). ▪