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1360 Section 11 Oncologic Disease

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Figure 155.1 A MCT at the mucocutaneous junction of the nasal Figure 155.3 A population of Diff‐Quik stained round cells at 40×.
planum. Tumors in this location often are biologically more Notice the lack of consistent granules and cellular atypia (multiple
aggressive with increased metastatic potential. nucleoli, varying N:C ratio, etc.). Alternative cytologic staining
techniques (Wright’s) are more adept at identifying the granules
in high‐grade MCT.

tumors may result in a cytologic diagnosis of “round cell
tumor” (Figure 155.3). It is important to remember that
cytology is ineffective in grading a MCT but the level of
cellular pleomorphism may provide clues to the biologic
behavior of a tumor.
Staging is important as both prognosis and treatment
options are intimately dependent on it (Box 155.1). Initial
staging of a MCT is dependent on physical exam findings.
Close attention should be paid to the regional draining
lymph nodes and organomegaly (hepatic and/or splenic).
Regional lymph nodes, regardless of size, should be
cytologically evaluated for metastasis. The determina-
tion of lymph node metastasis via cytology is very sensi-
tive but has a low specificity due to the inability to
Figure 155.2 Mast cells seen at 40× with varying amounts of distinguish normal, responsive mast cells from malig-
metachromatic granules throughout the cytoplasm.
nant cells. Metastasis can be accurately confirmed
if mast cells are the predominant cell type. Additionally,
diameter is not indicated. While Darier’s sign may most pathologists will declare a node metastatic if
develop, significant systemic histamine effects are the mast cells are noted in clumps or sheets and/or have
highly unlikely with simple dermal lesions. Cytology marked cellular atypia. Biopsy or removal of the lymph
of larger masses, or more vascular organs like lymph node is recommended if there is an increase in the num-
node and spleen, does justify systemic protection with bers of well‐granulated mast cells but no other signs sup-
antihistamines. portive of metastasis. Recent evidence supports that
Mast cells are mononuclear round cells with a signifi- dogs with no metastasis to regional nodes had a 0%
cant amount of cytoplasm containing metachromatic chance of distant metastasis.
granules. For comparison, mast cells range in size between Abdominal ultrasound is recommended for dogs
a neutrophil and macrophage. Diff‐Quik staining tech- with a high‐grade MCT or proven lymph node metasta-
niques are usually adequate in accentuating the diagnos- sis. While a full abdominal ultrasound is encouraged,
tic granules (Figure 155.2). When collecting samples, it is focus should rest on the liver, spleen, and lymph nodes
important to save an unstained slide for alternative stain- (mesenteric, medial iliac, and sublumbar nodes). All
ing techniques (i.e., Wright’s) if mast cells are suspected abnormal lesions of the liver and spleen should be
but granules are not identified with Diff‐Quik stain. cytologically evaluated. Two independent studies con-
Without appropriate staining, these poorly granulated firmed that cytology of ultrasonographically normal