Page 147 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

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Diagnostic Cytopathology in Clinical

Oncology

KRISTEN R. FRIEDRICHS AND KAREN M. YOUNG

In veterinary oncology, cytologic evaluation plays several impor- features of the tumor described. Staging procedures often include
tant roles that aid in clinical decision making, including making a cytologic evaluation of regional lymph nodes (LNs). Importantly,
preliminary or definitive diagnosis, planning diagnostic and treat- LNs containing metastatic disease are not always enlarged, and
ment strategies, determining prognosis through staging, detecting thus normal-sized LNs should be sampled. For detection of solid
recurrence, and monitoring response to therapy. An understand- tumor metastasis to regional LNs, fine-needle aspiration (FNA) is
1
ing of the advantages and limitations of cytologic evaluation is highly sensitive and specific ; however, metastatic disease may be
necessary to use this diagnostic modality effectively in clinical present even if tumor cells are not identified in a sample collected
oncology. from an LN; in this case, histologic evaluation may be required.
Advantages of cytologic evaluation include the ability to evalu-
ate the morphologic appearance of individual cells, the relatively Sample Collection
low risk of procedures to the patient, the lower cost compared
with surgical biopsy, and the speed with which results can be Proper collection and preparation techniques are prerequisites to
obtained. Cytologic evaluation also has several limitations. The obtaining diagnostic samples of high quality. Supplies necessary for
amount of tissue sampled is small compared with that obtained collecting cytologic samples from a variety of tissues, body cavities,
from a surgical biopsy; therefore cytologic specimens may not and mucosal surfaces are available in most clinics. These include
be fully representative of the lesion. Sample quality may be poor hypodermic needles and syringes, scalpel blades and handles, pro-
because of factors intrinsic to the lesion or poor collection tech- pylene urinary catheters, bone marrow aspiration needles, cotton
nique. Importantly, the inability to evaluate architectural relation- swabs, clean glass slides, marking pencils, and collection vials and
ships among cells in cytologic specimens may prevent distinction tubes (tubes with ethylenediaminetetraacetic acid [EDTA] and
between reactive and neoplastic processes or between benign and plain sterile tubes). For aspiration of internal lesions, obtained
malignant tumors. Examination of histologic samples, in which by guidance with ultrasonography or computed tomography
tissue architecture is preserved, may be required to make a defini- (CT), longer spinal needles and extension sets (used to connect
tive diagnosis of neoplasia, determine tumor type, and assess the the spinal needle to the aspirating syringe) are useful. Cytologic
extent of the lesion, including metastasis. Even then, ancillary specimens also can be made from tissues collected during surgical
tests such as immunohistochemical staining or tests for clonality biopsy (see Chapter 9). All supplies should be assembled in one
may be required. Often, cytologic evaluation precedes a surgical location for ready access. Although life-threatening situations are
biopsy and provides information that assists in formulating subse- rarely encountered when collecting cytologic specimens, supplies
quent diagnostic and treatment procedures. and medications should be available to control bleeding and to
Some tumors, such as lymphoma, may often be definitively treat anaphylaxis. The latter can occur rarely when aspirating mast
diagnosed and staged using cytologic evaluation exclusively, and cell tumors (MCTs) because of release of histamine.
treatment can be initiated without the need to collect histologic For external or easily accessible lesions, such as cutaneous and
specimens. For other tumors, such as well-differentiated hepato- subcutaneous masses or enlarged LNs, aspiration simply requires
cellular carcinoma, cytologic examination permits formulation of stabilization of the mass and consideration of underlying struc-
a list of differential diagnoses, and histologic evaluation must be tures, such as large vessels and nerves. Some large abdominal
performed for definitive diagnosis. At a minimum, categorization masses can be aspirated blindly if they can be stabilized and if they
of a tumor as an epithelial, mesenchymal, or discrete round cell are unlikely to be highly vascular or an abscess, aspiration of which
tumor often can be determined cytologically; this may be sufficient may result in hemorrhage or dissemination of infection, respec-
for initial discussions with the owner about diagnosis and prog- tively. Aspiration of intrathoracic and intraabdominal lesions is
nosis. Staging the malignancy, monitoring therapy, and detecting typically accomplished with guidance by imaging, either by ultra-
recurrence using cytologic evaluation are more easily accomplished sonography or by CT, to aid in targeting the lesion and avoiding
once a definitive diagnosis has been made and cytomorphologic large vessels and other sensitive areas. Defects in cortical bone also

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