Page 82 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

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The Pathology of Neoplasia

DEBRA A. KAMSTOCK, DUNCAN S. RUSSELL, AND BARBARA E. POWERS

Veterinary pathologists play a critical role in the management of Very small samples can be easily lost during shipping or in
companion animal neoplasia by providing diagnostic information processing because of sample shrinkage during fixation and pro-
that ultimately affects the prognosis and therapeutic decisions. The cessing. Given these considerations, some techniques can be used
clinician should have an understanding of how these diagnoses are to minimize tissue loss and maximize the likelihood of diagno-
generated and communicated, while also having an awareness of sis. Samples less than 3 mm in size can be placed on paper (e.g.,
the limitations of routine histopathologic assessment. A functional surgical glove paper) before fixation. These samples will be tacky
interdisciplinary working relationship between the pathologist and adhere to the paper. Very small or pale samples can be circled
and the clinician is essential to determine the optimal treatment with pencil to draw attention to the samples at the laboratory.
for the cancer patient, especially as the diagnosis and treatment of The paper can be folded around the sample, and the entire pack-
neoplasia in veterinary medicine continues to become more com- age can be placed in formalin for fixation and shipping. Alterna-
plex. The cell of origin (histogenesis), which indicates the tumor tively, commercially available screened tissue cassettes can be used
type, needs to be identified as accurately as possible, and tumor to house the sample during fixation and shipment. The sample is
subtypes should be identified, where applicable, especially when placed in the screened cassette at the time of surgery, and the cas-
prognostically significant. Histologic grading of tumors is increas- sette with the sample is placed directly into formalin for fixation.
ingly important, because for a number of tumor types, this has Extremely small samples can also be dyed with India ink or other
been shown to be a strong prognosticator of biologic behavior. commercially available dyes to assist in the identification of the
Evaluation of surgical margins to assess excisional completeness sample.
also is often a critical component that may significantly affect the If the specimen is an excisional biopsy, the entire sample should
prognosis and therapeutic direction. Ancillary diagnostics, such be submitted, if feasible, and margins of concern should be identi-
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as immunohistochemistry (IHC), immunocytochemistry (ICC), fied with suture or ink. If the entire mass cannot be submitted, it
transmission electron microscopy (TEM), flow cytometry, or is best to submit five or six sections, in the event some are nondi-
polymerase chain reaction (PCR) may be necessary to identify the agnostic. When representative samples are taken, regardless of the
tumor type or subtype correctly, to better estimate the prognosis, tumor site, sections from the tumor/nontumor interface should
or to predict the response to therapy. As research and discovery be included. This allows evaluation of the interaction of the tumor
continue in the field of veterinary neoplasia, prognostic and pre- with the surrounding normal tissue (e.g., invasiveness). If the cli-
dictive markers, in addition to tumor classification, for practical nician wishes to select sections that also contain surgical margins
application will continue to evolve. of interest, this should be explicitly stated on the submission form,
and the physical tissue margins should be definitively marked
Sample Handling (e.g., surgical ink). For large splenic tumors, multiple representa-
tive sections of solid or heterogenous tumor tissue, in addition to
Multiple steps are involved in sample handling, from tissue pro- regions at the tumor/nontumor interface, should be collected if
curement to the completed slide for the pathologist’s review. the entire spleen cannot be submitted; necrotic and hemorrhagic
Each step can affect the specimen’s quality and the final micro- areas that are friable and collapse easily on manipulation should
scopic interpretation. At the onset, the biopsy sample should be be avoided. Ultimately, caution should be used in handling all
visually inspected by the clinician to confirm that the appro- specimens; compression or crushing during the biopsy procedure
priate tissue has been obtained. If the biopsy is a needle-core or before fixation and excessive use of electrocautery, cryosurgery,
or incisional specimen, the sample should be of sufficient size or laser surgery all can cause specimen artifacts, which can reduce
and consistency that it remains intact in formalin and is not the sample’s quality and impede diagnosis, particularly in small
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lost in processing. Samples less than 1 mm are usually inad- specimens. 2,3,4
equate, although a needle-core sample 1 mm wide but at least Biopsy samples for routine histopathology need to be preserved
5 mm long can be sufficient. If the biopsy samples are needle- in a fixative. The most widely used fixative is 10% neutral buff-
core samples, more than one core of tissue should be obtained, ered formalin, which is readily available and frequently supplied
if possible. Samples composed of extensive blood, mucus, fat, in individual specimen containers by many laboratories. During
or necrotic debris are typically nondiagnostic and repeat biopsy excessively cold weather, samples can freeze during shipment,
should be considered. which causes significant destructive tissue artifact. The addition of

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