Page 447 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 22 Soft Tissue Sarcomas 425

vaccines, avoiding the use of aluminum-based adjuvants, and which is seen in young dogs. The distribution of STS in humans
increasing the interval between vaccinations. 26,177,263,264 is similar to animals. In humans, 43% are in the extremities, with
two-thirds occurring in the lower limb, and 34% are intraperito-
The VAFSTF has recommended that no vaccine be admin-
VetBooks.ir istered in the interscapular region, rabies vaccines be adminis- neal, with 19% visceral in origin and 15% retroperitoneal. STSs
of the trunk occur in 10% of human patients, and the remaining
tered in the distal aspect of the right pelvic limb, FeLV vaccines
be administered in the distal aspect of the left pelvic limb, and 13% occur at other sites. Metastasis is generally hematogenous
all other vaccines be administered in the right shoulder. 26,192 The and appears to be more common in human STS than in dogs,
location of each injection, the type of vaccine, and the manufac- which may partially be explained by the higher numbers of nerve
turer and serial number of the vaccine should be documented in sheath tumors (with lower metastatic rate) seen in the dog.
the patient records. These recommendations are intended to pro- Most sarcomas recognized in humans are also diagnosed in ani-
vide epidemiologic information rather than prevent ISSs. Vaccines mals, although the specific incidences may vary markedly. There
should be administered into the distal, rather than mid to proxi- are many more histologic subtypes recognized in humans, which
mal, aspects of the limb to aid in earlier detection and increase are often site dependent. With the exception of benign smooth
the chance of achieving complete resection. Subcutaneous and muscle tumors and subcutaneous lipomas, there is little evidence
intramuscular administration can both cause local inflammatory that these lesions arise from their mature (differentiated) tissue
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reactions and result in the development of ISSs. Subcutaneous counterparts. One current theory is that switching on a set of
administration is preferred to intramuscular injection because genes that programs mesenchymal differentiation in any mes-
ISSs developing from subcutaneous sites are more readily palpable enchymal cell may give rise to any type of mesenchymal tumor.
and diagnosed earlier in the course of disease. The VAFSTF has Common subtypes of STSs seen in the extremities of humans are
recommended that masses at vaccination sites be interrogated if liposarcomas, MFHs, SCS, and FSAs. In the retroperitoneal loca-
the mass is evident 3 or more months after vaccination, is larger tion, liposarcomas and leiomyosarcomas are the most common
than 2 cm in diameter, or is increasing in size more than 1 month histotypes noted in humans. The most common subtype noted
after vaccine administration (3–2–1 Rule). 191,192 Unfortunately, viscerally are gastrointestinal stromal tumors (GISTs). Overall,
feline ISSs are still occurring at sites not recommended by the leiomyosarcoma is the most common genitourinary sarcoma. Up
VAFSTF. 178,179,181,185 Vaccination in the tail has been recom- to 15% of all sarcomas occur in children, and the subtypes most
mended by some investigators because masses are more readily vis- commonly represented are rhabdomyosarcomas, Ewing’s sarco-
ible and palpable in the tail than other sites and the tail is relatively mas, and primitive neuroectodermal tumors.
simple to amputate with good margins and minimal effect on the Prognostic variables in humans include clinical stage, histo-
function and quality of life of cats, especially compared with other logic grade, necrosis, site, size, LN involvement, and aggressive-
locations such as interscapular resections, body wall resections, ness of surgery or RT. The histopathologic grading system used
and limb amputations or hemipelvectomies. 265 In a pilot study, and shown to be predictive for metastasis in dogs is a grading
vaccination in the tip of the tail was well tolerated and did not system adopted from human pathology that is also predictive for
require sedation or restraint. 265 survival. In addition, it appears that histologic grade is the pre-
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Traditionally, annual boosters have been recommended for dominant predictor of early recurrence, whereas tumor size plays a
most vaccines in cats. The U.S. Department of Agriculture–Ani- more important role for late recurrence. It is unclear whether age
mal Plant Health Inspection Service (USDA-APHIS) does not plays a prognostic role in human STS.
require duration of immunity studies for licensing of vaccines; Surgical treatment is the mainstay of therapy for STS in the control
however, if a duration of immunity study has not been performed, of local disease. The definition of the surgical approach varies between
the USDA-APHIS requires that vaccine labels include a recom- different organizations, with 1- to 4-cm lateral margins considered a
mendation for annual revaccination. 192 Vaccine practices have wide resection and those 5 cm or greater termed a curative resection;
been questioned by the profession and this has been supported however, tissue barriers are also taken into account in determining
by duration of immunity studies. The duration of immunity for surgical margins, with thin and thick tissue barriers being consid-
a single commercially available inactivated, adjuvanted combina- ered equivalent to 2 cm and 3 cm of margins, respectively. Surgery
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tion of feline panleukopenia, herpesvirus, and calicivirus is greater can be combined with neoadjuvant chemotherapy, neoadjuvant RT,
than 7 years, with persistent antibodies against all three viruses and/or adjuvant RT to improve local tumor control. Amputa-
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for more than 3 years. 266–268 Local and state requirements often tion is reserved for patients with unresectable tumors, no evidence
mandate annual rabies boosters, despite a duration of immunity of metastasis, and the potential for good long-term rehabilitation.
of at least 3 years, because of the significant public health concern Local recurrence is greater in those patients undergoing limb-sparing
of rabies infection. 192 The VAFSTF has recommended that the therapies compared with amputation; however, there is no difference
administration of vaccines is a medicinal procedure and vaccina- in disease-free survival between the two groups. Distant metastasis
tion protocols should be customized for individual cats. 192 A vac- is more common in people with STS; however, chemotherapy is
cine should not be administered until the medical importance and not routinely used because of either a lack of or small but significant
zoonotic potential of the infectious agent, risk of exposure, and improvements in tumor control and survival outcomes with adju-
legal requirements have been considered and balanced against the vant chemotherapy. Ifosfamide is currently the most active salvage
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risk of ISSs and other adverse effects. 192 agent for patients who have failed DOX-based protocols, but tyrosine
kinase inhibitors are also used. Permanent local control with the first
Comparative Aspects treatment is related to long-term survival. High-risk STS patients are
treated with combined chemoradiation before surgical resection. The
In general, STSs have a similar pathologic appearance, clinical chemotherapy protocol often used is DOX, ifosfamide, mesna, and
presentation, and behavior in humans and animals. However, a dacarbazine. In human patients with metastatic disease, combination
higher incidence is seen in young people as opposed to young chemotherapy produces response rates of 20%, and most of these
companion animals, with the exception of rhabdomyosarcoma, patients are candidates for investigational agents.