Page 83 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

62 PART I The Biology and Pathogenesis of Cancer

20% ethylene glycol or ethanol to the formalin can prevent freez- distinction between benign and malignant processes can be deter-
ing and maintain tissue integrity. Before immersion in fixative, mined. Frozen-section diagnoses are always confirmed by routine
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histopathology, often using the same tissue sample.
larger samples may need to be partially sectioned (bread-loafed)
VetBooks.ir to facilitate appropriate fixation, which is critical to preserve commonplace in veterinary medicine and can be performed on
Molecular-based tests, such as IHC and PCR, have become
microscopic tissue architecture; one side, such as the deep edge,
should be left intact to retain tissue orientation. Slices less than FFPE tissue. These samples often are viable indefinitely for these
1
1 cm thick should be avoided because the fixed tissue may curl tests, although the time before fixation, time in fixation, fixative
and distort. The volume of tissue to fixative should approximate used, and storage time can negatively affect test performance.
1:10. If this is not feasible because of large tumor size, multiple Exposure to sunlight or extreme temperatures during storage
representative sections can be submitted. The remaining biopsy should also be avoided. Such factors should be considered in the
sample should be retained in formalin, if possible, in case prelimi- interpretation of results. Individual laboratory guidelines for the
nary sections are nondiagnostic. When large samples are mailed, samples required and shipping methods used should be followed
smaller volumes of fixative may be adequate if the specimen has to ensure optimal results. IHC requires unstained FFPE tissue
been in the recommended initial volume for at least 12 hours, or sections on positively charged slides. PCR typically requires thick
the sample can be shipped chilled (without fixative) if previously sections (10–20 μm FFPE curls) containing ample nonnecrotic
in fixative for 48 to 72 hours. 1 tumor tissue to assure adequate DNA or RNA amounts. These
Submissions must include the biopsy sample and all necessary can be sent to the testing laboratory at room temperature in an
paperwork. Sample containers (not just the lid), must be properly airtight container.
labeled because samples can inadvertently become separated from
submitted paperwork. A critical determinant of accurate biopsy Terminology
results is the information provided by the clinician, typically on the
1
submission form. This information should include, but is not The word tumor is derived from the Latin word for swelling
limited to, signalment, relevant clinical history, clinical findings, (tumere: to swell), which initially was recognized as a hallmark
disease progression, imaging results, treatments (prior treatments of inflammation in the 1st century. In modern usage the term
can affect tissue/cellular features microscopically), clinical impres- tumor typically refers to a neoplasm, which may be benign or
sion, and primary clinical differentials. The pathologist uses this malignant. Neoplasia is the formation of a new, abnormal growth
information to generate and validate the microscopic diagnosis (or of a tissue that is not responsive to normal physiologic control
differential diagnoses). Without this, the diagnosis and/or prog- mechanisms and may be benign or malignant. The growth of this
nostic interpretation may be inaccurate, culminating in improper mass is not affected when the inciting stimulus is removed. Cancer
patient management. Clear communication of the anatomic specifically refers to a malignant neoplasm. Benign tumors can be
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location, which may include a photograph or drawing, is also space occupying and can cause tissue distortion; however, they do
important, especially in the consideration of specific tumor types not metastasize or have a high mortality. In contrast, malignant
(e.g., periarticular neoplasia), the prognosis (e.g., melanoma of the tumors (cancer) are more locally destructive, have the potential to
nail bed versus other cutaneous sites), and margin determination. metastasize, and may lead to death if left untreated.
If margins or areas of special clinical interest are marked on the All neoplasms arise in normal tissue and thus are composed
sample, a clear description of these markings should be included of parenchymal and stromal cells; some may also be associated
on the submission form. with inflammation. Tumor histogenesis and differentiation can be
Once at the laboratory specimens are accessioned, visually assessed with histopathology; they are based on the appearance of
examined, trimmed into processing cassettes, processed into par- the tumor cells, their organization, and their association with the
affin blocks, sectioned, and stained. In most laboratories com- supporting stroma. Differentiation is controlled at the molecu-
pleted slides are ready for examination by the pathologist 24 to 48 lar level by gene expression. The potentially reversible process of
hours after receipt. Samples such as bone require decalcification hyperplasia (a nonneoplastic increase in the number of cells pres-
before trimming and sectioning and therefore take longer to pro- ent) is also composed of parenchymal cells and stroma. Retention
cess. Larger samples that are incompletely fixed, extremely bloody of near-normal architecture, similar to well-differentiated neo-
samples (e.g., spleen), or samples with abundant fatty tissue (e.g., plasms, can make distinguishing between hyperplasia and benign
mammary gland) may also require additional time for fixation. neoplasia difficult. Neoplasia can also be defined as clonal expan-
Once the specimen has been trimmed, most laboratories hold the sion (uncontrolled proliferation of a clonal population of cells) that
remaining “wet” (fixed) tissues for a specified period in the event is no longer responsive to homeostatic mechanisms. Molecular
further evaluation is needed. Many laboratories file formalin-fixed techniques to determine clonality, such as PCR for antigen recep-
paraffin-embedded (FFPE) tissue blocks and/or glass slides for tor rearrangement, can help differentiate these conditions. These
prolonged periods, which allows for case review, additional diag- tests are best recognized for use in canine and feline lymphomas. 7
nostics, or retrospective case studies. Metaplasia is the transformation of normal differentiated tissue
Although the technique is infrequently used, frozen sections of one kind into differentiated tissue of another and is not neo-
can provide the surgeon with a more rapid diagnosis. Samples are plastic. Metaplasia can reverse with cessation of the chronic incit-
quick-frozen, sectioned on a cryostat, fixed, stained, and examined ing stimulus. An example is squamous metaplasia of the columnar
within 20 to 35 minutes. This technique is typically performed epithelium of the prostate gland under the influence of estrogen.
during surgery to assist with intraoperative decisions; essential If stimuli persist and promotional events occur, metaplastic cells
requirements are appropriate equipment on site and a pathologist can become targets for carcinogenesis (e.g., bronchial squamous
with expertise in interpreting frozen sections. Frozen sections may metaplasia in human smokers). In such cases metaplastic cells
be helpful in establishing the identity of the tissue, completeness often acquire dysplastic changes. Dysplasia refers to abnormal epi-
of excision, or adequacy of the tissue for more routine process- thelial growth and differentiation and can be a feature of neopla-
ing. Sometimes a provisional diagnosis can be made, or at least a sia, but it is not necessarily a neoplastic condition. Dysplasia, such