Page 157 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

136 PART II Diagnostic Procedures for the Cancer Patient

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• Fig. 7.16 Fine-needle aspirate of a thymoma in a dog. The majority of • Fig. 7.17 Fine-needle aspirate of a thyroid carcinoma in a dog. Note the
cells are small lymphocytes. A mast cell and an eosinophil also are present. loosely cohesive sheets of cells in a background of free nuclei and abun-
dant blood. Inset: Some of the tumor cells contain blue-black granules
thought to be tyrosine granules.
arranged individually or in small sheets. Criteria of malignancy
among the epithelial cells are minimal in thymomas. Histologic
examination or molecular diagnostic tests (e.g., flow cytometry)
are often necessary to confirm a thymoma diagnosis (see Chapter
34, Section B). In thymic carcinomas, the epithelial component
is much more prominent as are criteria of malignancy.

Nasal Carcinomas and Adenocarcinomas
Nasal carcinomas and adenocarcinomas, like primary lung tumors,
typically are only mildly to moderately pleomorphic. Cytoplasmic
vacuolation also may vary, with the majority of cells having few-
to-no secretory vacuoles. Apical cilia are typically lacking. Small
numbers of highly pleomorphic epithelial cells arranged in sheets
or clusters accompanied by marked neutrophilic inflammation
likely represent hyperplastic respiratory epithelium and not a
tumor. Surgical biopsy is often required to make a diagnosis of
neoplasia, especially when cytoplasmic features are not definitive
and when concurrent inflammation is present.
• Fig. 7.18 Fine-needle aspirate of anal sac apocrine adenocarcinoma.
Gastrointestinal Tumors Note the rosette of tumor cells (right). Mild anisokaryosis and a macro-
Epithelial gastrointestinal tumors include adenocarcinomas of the nucleus are seen (left), although this tumor is typically monomorphic.
stomach, small intestine, and large intestine, and these tumors have
similar cytologic features. Aspirates of these tumors typically consist not known, a specific tumor type may be impossible to deter-
of highly pleomorphic epithelial cells arranged in sheets and clus- mine owing to the cytologic similarity among these tumors. In
ters. The cells typically contain few-to-many secretory vacuoles. The general, aspirates of endocrine and neuroendocrine tumors are
background may contain abundant mucus produced by the tumor highly cellular and consist of loosely cohesive sheets and clusters
cells or pink fibrillar collagen representing a scirrhous response of epithelial cells with ill-defined intercellular junctions and cyto-
secondary to the tumor. Anaplastic carcinomas of the gastroin- plasmic margins (Fig. 7.17). The cells are fragile, and numerous
testinal tract may resemble discrete round cell tumors (Fig. 7.8). free nuclei from ruptured cells are scattered in the background.
Polyps may occur anywhere in the gastrointestinal tract and typi- Nuclei of intact cells may be arranged in a rosette (Fig. 7.18),
cally have a benign cytologic appearance with uniform, hyperchro- suggestive of acinar formation. Within intact cells, nuclei are
matic cuboidal to columnar epithelial cells arranged in dense sheets. round and centrally located with reticular chromatin. Nucleoli
Occasional goblet cells with a large pale blue cytoplasmic inclusion are often indistinct, but one to two nucleoli may be observed.
may be observed. Histologic examination of a full thickness surgical The cytoplasm may contain a few clear, distinct vacuoles. There
biopsy is required to definitively differentiate invasive carcinomas are usually few criteria of malignancy, even in carcinomas, and
and carcinoma in situ from noninvasive polyps. anisocytosis and anisokaryosis are mild to moderate, with large
nuclei observed occasionally. Mitotic figures may be present.
Endocrine and Neuroendocrine Tumors Some tumors of endocrine origin are biologically active, and
Endocrine and neuroendocrine tumors comprise a diverse col- tumor type may be identified based on clinical presentation and
lection of tumor types. If the primary location of the tumor is laboratory findings.