Page 86 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 3 The Pathology of Neoplasia 65

TABLE 3.2 Histologic Features of Hyperplasia and Benign and Malignant Neoplasia
Histologic Feature Hyperplasia Benign Neoplasia Malignant Neoplasia
VetBooks.ir Tissue demarcation Blends with normal Expansive and/or compressive, possibly Invasive, infiltrative, unencapsulated, poorly
tissue
encapsulated, well demarcated
demarcated
Organization/architecture of Retention of normal Fairly uniform, typically some retention Moderately to markedly haphazard, loss of normal
cell population tissue architecture of normal architecture architecture
Cellular differentiation Normal Well differentiated Moderately to poorly differentiated or undiffer-
entiated
Cell and nuclear pleomorphism None Minimal Moderate to marked
Cellular and nuclear atypia None Minimal to none Moderate to marked; binucleated, multinucleated,
karyomegalic, or bizarre nuclei may be observed
Anisocytosis/anisokaryosis None Minimal to none Moderate to marked
Nucleoli Normal, indiscernible Normal, typically indiscernible Prominent, large and/or multiple
Mitotic figures Typically low Typically low a Typically high a
Necrosis None Minimal to none Moderate to marked
Stromal reaction None None Scirrhous or desmoplastic response b
Vascular invasion (blood or Not present Not present Potential to exist
lymphatic vasculature)
a Exceptions exist; see Table 3.3.
b Especially as can be seen with squamous cell and transitional cell carcinoma.

Histopathologic features that distinguish benign from malig- chemotherapy, or a combination thereof) because histopathologic
nant neoplasia were introduced in the earlier section Terminology features of treatment-associated tissue responses can be difficult
and in Table 3.2. Ultimately, malignancies typically are charac- to distinguish from overt neoplasia. This may be especially true
terized by invasive growth with effacement of normal tissue and after RT, which can induce the formation of bizarre reactive cells,
poor organization of the tumor tissue itself. Cellular features of including fibroblasts (radiation atypical fibroblasts), that display
malignancy include increased cellular and nuclear pleomorphism; many features of malignancy, although these cells are not neoplas-
increased anisocytosis and anisokaryosis; increased and variable tic. Inflammation, fibrovascular proliferation, and EC and/or
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nuclear:cytoplasmic ratio; presence of binucleated, multinucle- epithelial hyperplasia are other possible treatment-associated tis-
ated, and/or karyomegalic cells or bizarre nuclei; abnormal nuclear sue responses that may preclude or obscure an appropriate assess-
chromatin; increased number of mitotic figures; bizarre mitotic ment of neoplasia. If tumor cells are identified, the clinician may
figures; and abnormal, large, prominent and/or multiple nucleoli. wish to know if these cells are viable, dead, or rendered viable but
Increased necrosis also is recognized as a feature of malignancy. sterilized (reproductively dead) by RT or chemotherapy. Although
Unequivocal intravascular (hematogenous or lymphogenous) the latter is not possible with routine microscopy, the presence of
invasion, histologic evidence of lymph node (LN) involvement, mitotic figures in the tumor cell population would indicate repli-
or widespread metastasis (confirmed by submission of multiple cative potential.
lesions at various sites) conclusively establish malignancy, regard-
less of other histopathologic features. 2,5,14 Mitotic Figures
In some tumors the histopathologic features do not correlate
with expected biologic behavior. Examples include canine cutane- Mitotic figures (MFs) are observable, quantifiable tumor-associ-
ous histiocytoma, benign plasmacytoma, and pleomorphic feline ated histopathologic features that have been proven to be a reliable
cutaneous MCT. 15–17 These typically display some histologic fea- prognostic indictor for some tumors. The terminology, methodol-
tures of malignancy but clinically are benign. Histologically low- ogy of acquisition, and reporting of MFs, however, has varied over
grade yet biologically high-grade FSAs of the canine oral cavity the years and thus is addressed here to provide the clinician with
have benign histologic features but are clinically malignant. some insight and guidance when interpreting the MF information
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Similarly, bronchial carcinomas in cats retain organized epithe- provided in the pathology report.
lial structures composed of well-differentiated, ciliated, pseu- A MF provides visual confirmation of an actively dividing cell,
dostratified columnar epithelium even at distant metastatic sites, specifically in mitosis. Mitosis occurs during the M-phase when
including the digit, eye, heart, and kidneys. In these instances replicated chromosomes of the cell are separated into two sepa-
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knowledge of the clinical history and tumor behavior is essential rate nuclei and, ultimately, cytokinesis gives rise to two separate
to distinguish benign from malignant neoplasia. cells. Mitotic stages are divided into prophase, prometaphase,
Challenges may also be encountered during evaluation for pos- metaphase, anaphase, and telophase, any of which may be visual-
sible recurrence after therapy (surgery, radiation therapy [RT], ized on routine microscopic evaluation, and all are considered