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core biopsy (TNCB) specimens should be obtained. TNCB is the easiest and fastest method and requires minimal sedation. Multiple core biopsies should be performed and submitted to the pathologist. Sufficient tissue, however, is often better acquired by incisional or excisional biopsies. Excisional biopsies are only advantageous when adequate margins can be obtained. In all other cases an incisional biopsy is preferred. Normal tissue should be incorporated in the biopsy specimen to evaluate peripheral infiltration
An Urban Experience
original tumor will facilitate complete removal and prevent recurrence. Shelling out the tumor is the most common cause for recurrence. Education and communication should be directed in the future to achieve these goals of early detection and complete removal.
Overall metastatic rate is estimated to be 20%. Among subtypes there exists considerable variation. In part, this appears based on a link between subtype and frequency distribution of histologic grade. Low to moderate rate of metastasis is seen in (mostly low grade) tumours. More undifferentiated STS have a higher rate of metastasis, i.e., 4060%. Metastastatic spread by lymphatic routes and lymph node involvement is reported to be rare STS. High-grade tumours have a higher incidence of lymphatic spread especially in late stages of the disease.
Treatment
Surgery is the primary therapy of STS, with or without adjunctive therapy. The surgical goal is to completely remove the tumor and, as a result, a large margin of normal tissue is sacrificed. An example of this type
of surgery is the amputation of a limb. Limb-sparing surgeries are an alternative, but can only be performed in combination with adjunctive therapy modalities such as radiotherapy, chemotherapy and immunotherapy in case of large tumor mass.
Surgery
Surgery is only successful if large margins of normal tissue are obtained, with margins of 2-3 cm normal
tissue advocated. The objective local failure rate for marginal excisions (peel-out or shelling-out) in humans
is 86%; however, these rates, based on large numbers, are unknown in dogs and cats. Failure rates after wide local excisions and more radical excisions (such as amputations) were 49% and 14% in humans, respectively. Extrapolation from human data is tempting, but should
be interpreted with caution. Recurrence rates of 60-70% are reported in marginally excised STS. Although most STS tend to recur within a year after surgery, adequate follow-up of 2 to 3 years is necessary. Wide surgical excision is often complicated by the anatomic localisation of the tumour to important structures. In general, a repeat surgery is more complicated if the tumor has recurred and failure is more likely. The first surgery has the largest chance for complete removal. Recurrence, as of yet,
is not associated with an increased risk of metastases, however. It is the authors’ opinion that the incidence of metastases depend more on tumour grade than on the type of surgery performed. The recurrence rate decreases when the surgery is performed by more experienced oncologic surgeon. Experience often correlates to
a more radical surgery, knowledge of innovative reconstruction techniques and better understanding of the pathophysiological properties of the tumour.
of the tumour. Incisional biopsies should always be performed in such a manner that removal of the scar is possible in future radical excisions or adjunctive radiation therapy protocols. Adjunctive diagnostic evaluations should include routine blood work, radiographs of the local tumour site for possible underlying bone infiltration, ultrasound of the tumour, radiographs of the chest for possible metastatic spread, FNAB of the regional lymph node and CT or MRI imaging techniques.
The most important factors in STS evaluation are the determination of tumour grade and tumour stage. Tumour grade is determined through histological evaluation and varies among grade I (low grade or
well differentiated) to grade III (high grade or poorly differentiated). Tumour grade is determined by degree of differentiation, cellular pleiomorphism, cellularity and matrix formation, as well as mitotic index and amount of tumour necrosis.
In human sarcomas, the tumour grade has a major impact on tumour staging. Tumour staging is based
on four parameters: histological grade (G), tumour size (T), regional lymph nodes (N), and distant metastasis (M) (Table 2). Factors reported to be of prognostic importance in canine STS are size, site, grade and presence of local or distant metastases. The prognostic effect of localisation of the tumour is most likely dependent on the difficulty of complete excision. Prognostic significance is closely correlated to tumour grade; the least differentiated tumours have the worst prognosis. Additionally, the higher the stage of the disease, the poorer the prognosis.
GENERAL CONSIDERATIONS
STS pose a problem to the veterinarian mainly because they tend to be locally aggressive. Complete surgical excision is often impossible because of localisation
or size of the tumour. Recurrence is common after incomplete resection and is the primary reason to refer these tumours to a specialised Surgical Oncology Service. Most recurrences will occur within 2 years after primary tumour removal. Recurrence is caused because STS tend to spread into deeper or surrounding tissues by invasion or extension next to natural anatomic structures. Cutting of the tumour mass leaves these tumour extensions in
the patient. Through this, the tumour homeostasis is disrupted and fast growing tumour cells thrive causing fast tumour regrowth. Early detection and diagnosis of the
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