Page 377 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 19 Tumors of the Skin and Subcutaneous Tissues 355

History and Clinical Signs these techniques are still being developed in veterinary medicine.
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Despite careful evaluation of a cytology sample, it is possible to
underestimate metastatic disease. Because of the unreliable nature
Tumors of the skin are often noticed by pet owners and brought to
VetBooks.ir their veterinarian’s attention. The biologic history of these masses of LN cytology and the potential effect of LN metastasis on the
prognosis and adjunctive therapy, histopathology should be consid-
can be quite variable. Self-trauma or secondary infection may cause
a patient to be presented for evaluation. Ultimately, however, it is ered in cases with a high risk of malignancy. 78,80
critical to remember that physical examination cannot definitively Evaluation of the patient for distant metastatic disease before
determine whether a lesion is benign or malignant – cytology or histopathologic confirmation of a neoplastic process is based on the
histopathology is necessary to diagnose any skin tumor. degree of suspicion that the mass is malignant, in addition to the
desires and financial limitations of the owner. After confirmation
Diagnostic Techniques and Workup of a malignant process, additional staging for detection of distant
metastatic disease and evaluation of overall suitability for proposed
The evaluation of a skin tumor is generally similar to the evaluation treatments are indicated. Such staging may include three-view tho-
for any solid tumor. A complete history can be very informative. racic radiographs, thoracic CT, abdominal ultrasound, and/or addi-
Careful elucidation of the duration, rate of growth, and clinical signs tional tests as indicated by the tumor type and clinical findings.
associated with the tumor may be helpful in differentiating benign
from malignant masses. The clinical evaluation of any patient with
a mass involves two steps: diagnosis and staging. Many cutaneous Treatment and Prognosis for Specific
and subcutaneous masses can be diagnosed with fine-needle aspira- Tumor Types
tion and cytology or direct impression cytology of a lesion. Cytol-
ogy is an inexpensive and relatively noninvasive means of diagnosing Given the external location of most skin and subcutaneous tumors,
many common benign skin tumors, such as lipomas or sebaceous the primary treatment option for achieving local control is surgery.
adenomas. For lesions that appear malignant or are nondiagnostic on For benign masses, marginal excision may be adequate to achieve
cytology, histopathology may be necessary. In addition to confirming long-term control. For malignant tumors, adequate surgical exci-
a diagnosis, histopathology yields useful information on the histologic sion requires a margin of normal tissue around the neoplasm. For a
grade of some tumors, such as MCTs, or the malignant behavior of a pathologist to determine whether excision is complete, all surgical
tumor, such as vascular and lymphatic invasion. Other characteristics, margins must be identified with surgical ink or sutures to ensure
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such as degree of differentiation, nuclear morphology, and percentage correct reporting of margins (see Chapter 10). The surgeon must
of necrosis, may be helpful with certain tumor types. properly prepare the sample to allow the pathologist to report all
The type of biopsy performed usually is dictated by the location critical information, including margin evaluation (see Chapter 3). 81
of the mass. Where wide surgical excision is feasible without undue Likewise, to report the tumor grade accurately in tumors for
morbidity, the biopsy can be combined with a therapeutic proce- which a grading scheme has been validated, a pathologist needs
dure (e.g., excisional biopsy), provided this approach does not affect a reasonably sized piece of tissue to evaluate. Needle-core or Tru-
definitive surgical excision if a malignant process is identified. How- Cut biopsies often yield limited amounts of tissue and should be
ever, in most instances the biopsy is a diagnostic test. The authors’ limited to tumors for which they are the only option.
preference for a biopsy of a skin or subcutaneous mass is multiple The most common cutaneous and subcutaneous tumors, mela-
punch biopsies or an incisional biopsy. (See Chapter 9 for a more nomas, MCTs, and soft tissue sarcomas (STSs) are discussed sepa-
detailed discussion of biopsy techniques.) These techniques allow rately in Chapters 20, 21, and 22, respectively. The remainder of
the procurement of a sufficiently large piece of tissue for an accurate this chapter covers the additional skin tumors, focusing on those
diagnosis and, where applicable, grading of the tumor. In addition, with malignant behavior.
the use of advanced histopathologic techniques, such as IHC for
evaluation of prognostic markers, can be performed. Some molecu-
lar tests, such as PCR, can be carried out on formalin-fixed tissues. Epithelial Tumors
Staging involves determination of the extent of disease locally, Tumors of the Primitive Follicular Epithelium
regionally, and distantly. Assessment of the primary tumor’s size by
measuring the longest diameter is the first step in the staging process. The term basal cell tumor was used for many years to include BCCs,
For large, infiltrative or fixed masses, local assessment may require basal cell epithelioma, trichoblastoma, and solid-cystic ductular sweat
advanced imaging, such as a computed tomography (CT) or mag- gland adenomas and adenocarcinomas. Because of progress in the
netic resonance imaging (MRI), to accurately determine the tumor’s ability of pathologists to differentiate these tumors on the basis of ker-
size and extent. One study demonstrated that the use of advanced atin and other membrane markers, trichoblastomas and solid-cystic
local imaging techniques increased the stage of the primary tumor ductular sweat gland tumors are no longer considered BCTs. Conse-
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in 69% of patients. Regional staging involves the assessment of quently, older studies that reported high rates of BCT, particularly in
the draining lymph node(s) (LN). Determination of the draining cats, may not reflect diagnostic patterns today. These related tumor
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node can be difficult for some locations, so evaluation of all LNs types are believed to arise from stem cells in the outer follicular root
in the region may be necessary. Radiographic or CT lymphogra- sheath displaying variable differentiation, although the origin for all
phy may be helpful for determining the sentinel LN when drainage tumors in this category cannot be absolutely identified.
patterns are unclear (see Chapter 9). 75,76 LN palpation is a poor Basosquamous cell carcinoma is a tumor with characteristics of
predictor of metastasis because metastatic LNs may be normal in both BCC and SCC. Immunohistochemically basosquamous cell
size and consistency. 77,78 Conversely, large, firm LNs may be reac- carcinomas are more closely related to BCCs and so are discussed
tive in response to an infection or inflammatory process. Aspiration in this section. Trichoepitheliomas are a more differentiated form
and cytologic examination by an experienced clinical pathologist is of the trichoblastoma. The most appropriate nomenclature and
critical for the assessment of regional LNs for evidence of metasta- classification schema for this group of tumors remains controver-
sis. IHC may also be more accurate for identifying metastasis, but sial. Tumor types are presented as categorized in the Armed Forces