Page 1288 - Small Animal Internal Medicine, 6th Edition

1260 PART XII Oncology

sizes); nuclear molding (i.e., a nucleus in a multinucleated basis of the predominant cytologic features, malignancies
cell is compressed by a neighboring one); morphologic can be classified as carcinomas (epithelial), sarcomas (mes-
VetBooks.ir homogeneity (i.e., all cells look alike); pleomorphism (i.e., enchymal), or round (or discrete) cell tumors (Fig. 74.3).
cells in different stages of development); vacuolization (pri-
Carcinomas
marily in malignant epithelial tumors); anisocytosis (i.e.,
cells are of different sizes); multinucleated giant cells; and, Most carcinomas are composed of round or polygonal cells
occasionally, phagocytic activity. Another feature of malig- that tend to cling together, forming clusters or large sheets.
nancy is heterotopia (i.e., the presence of a given cell type Their cytoplasms are usually deep blue, and in most adeno-
where it is not found anatomically); for example, relevant carcinomas vacuolization is evident. Cytoplasmic boundar-
numbers of epithelial cells can appear in a lymph node only ies are difficult to recognize, and the cells resemble a mass of
as a consequence of metastasis from a carcinoma. In addi- protoplasm rather than a sheet of individual cells. In squa-
tion, malignant cells tend to be morphologically different mous cell carcinomas, cells usually appear individualized,
from the progenitor cell population (see Box 74.1). On the can be irregular or polygonal, have a deep blue cytoplasm
(with an occasional eosinophilic fringe), and have large vac-
uoles; neoplastic cells in squamous cell carcinomas fre-
BOX 74.1 quently exhibit leukophagia. Nuclei in both adenocarcinomas
and squamous cell carcinomas are large, with a fine chroma-
Cytologic Characteristics of Malignant Neoplasms
tin pattern and evident nucleoli (Fig. 74.4).
Large nuclei
Fine chromatin pattern Sarcomas
One or more nucleoli The cytologic features of sarcomas vary according to the
Anisokaryosis histologic type. As a general rule, sarcomas do not exfoliate
Nuclear molding well; however, hemangiopericytomas and other spindle cell
Monomorphism sarcomas exfoliate so well that the clinician’s first impression
Pleomorphism on evaluating a smear may be that of a carcinoma (i.e., the
Anisocytosis cells appear to be in groups) (Fig. 74.5). Most mesenchymal
Cytoplasmic vacuolization
Cytoplasmic basophilia tumors have spindle-shaped, polygonal, polyhedral, or oval
Multinucleated giant cells cells, with a reddish-blue to dark blue cytoplasm and irregu-
Phagocytosis larly shaped nuclei. Most cells are individualized, although
Heterotopia clumping may occur (particularly in impression smears or
when a large-bore needle is used for sample collection). The

Criteria for neoplasia

Cells in clumps Round cells Spindle or polyhedral,
or sheets individual cells

Carcinoma Round cell tumor Sarcoma

Granules Vacuoles Neither

MCT (purple) TVT LSA
LGL (reddish) HCT HCT
MEL (black, gold, green) PCT

FIG 74.3
Flow chart for the cytologic diagnosis of tumors in dogs and cats. HCT, Histiocytoma;
LGL, large granular lymphoma; LSA, lymphoma; MCT, mast cell tumor; MEL, melanoma;
PCT, plasma cell tumor; TVT, transmissible venereal tumor.