Page 161 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

140 PART II Diagnostic Procedures for the Cancer Patient

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• Fig. 7.27 Fine-needle aspirate of a gastrointestinal stromal tumor (GIST). • Fig. 7.28 Fine-needle aspirate of a proliferative and lytic lesion in bone.
Many cells are disrupted, but elongated (cigar-shaped) nuclei are visible. The diagnosis was osteosarcoma. The pleomorphic cells tend to be round
or oval with eccentric nuclei and sometimes paranuclear clear zones.
Tumors of Striated Muscle Inset: A multinucleated tumor cell contains prominent pink granules.
Tumors of striated muscle, rhabdomyoma and rhabdomyosar-
coma, are uncommon and can have a variety of cytomorphologic
appearances. Rhabdomyomas occurring in the tongue and phar-
ynx may present cytologically as a “granular cell tumor” composed
of individual round or polygonal cells containing numerous fine
pink cytoplasmic granules and a central round nucleus. Electron
microscopic examination reveals the pink granules to be numer-
ous mitochondria. Rhabdomyosarcomas typically comprise indi-
vidualized pleomorphic spindle cells with low numbers of elongate
strap cells that may or may not demonstrate cross-striations within
the cytoplasm. Strap cells characteristically have several round-
to-oval nuclei arranged in a linear row. Normal muscle fibers are
bright blue, with prominent cross-striations when viewed at high
magnification, and have randomly distributed pale oval nuclei.
Mesenchymal Tumors Composed of Round or Oval Cells
Tumors of Bone Origin
Tumors of bone origin include osteosarcoma, osteoma, multilobu-
lar tumor of bone, and giant cell tumor of bone. Osteosarcoma • Fig. 7.29 Fine-needle aspirate of a chondrosarcoma with pleomorphic
(OSA) is the most common tumor of bone in dogs and results tumor cells and abundant magenta matrix that sometimes surrounds the
in a mixed osteolytic and osteoproliferative lesion radiographically. tumor cells (inset).
Aspirates of OSA may be highly or poorly cellular, depending on
the collection technique and the nature of the lesion. Cytologic with eccentric nuclei and paranuclear clearing; for inexperienced
features that support osteoblasts as the cells of origin include oval clinicians, this may constitute a diagnostic dilemma in dogs, and
cells with basophilic cytoplasm containing paranuclear clearing, less frequently in cats, that have osteolytic lesions. Clinical presen-
and eccentric nuclei with criteria of malignancy (Fig. 7.28). The tation and laboratory abnormalities may be useful in distinguishing
cytoplasm occasionally contains fine-to-coarse magenta granules these malignancies. Caution is recommended when making a cyto-
or few small clear vacuoles. N:C ratios are moderate to high, and logic diagnosis of OSA at the site of a pathologic fracture as hyper-
anisocytosis is moderate to occasionally marked. Alkaline phospha- plastic and reactive osteoblasts may have a degree of pleomorphism
tase staining of cytologic samples has been shown to differentiate that can be mistaken for a well-differentiated neoplasm.
tumors of osteoblast origin (osteosarcoma and multilobular tumor
of bone) from other vimentin-positive tumors of bone. Often, Tumors of Chondrocytes
bright magenta extracellular matrix or osteoid is found. Large mul- Tumors of chondrocytes are less common than osteosarcoma
tinucleated osteoclasts are typically scattered among the neoplastic and may arise in any location where cartilage occurs, including
osteoblasts. Multilobular tumor of bone and giant cell tumor of epiphyseal bone, nasal cavity, and large airways. Although the
bone are composed predominantly of osteoblasts and osteoclasts, amount of matrix present in any given tumor can vary, the most
respectively. In giant cell tumor of bone (or osteoclastoma), spindle characteristic cytologic finding in aspirates of chondrosarcoma is
cells are found; it is possible these cells, rather than the osteoclasts, the large amount of purple extracellular matrix that envelops and
may be the neoplastic cells. Both tumors have characteristic loca- often obscures the neoplastic chondroblasts (Fig. 7.29). Neoplas-
tions or radiographic appearances. The cytologic appearance of tic chondroblasts are round with moderate-to-high N:C ratios but
plasma cell tumor and OSA may overlap because both contain cells may be spindle or stellate. A few cytoplasmic vacuoles or magenta