CHAPTER 33 MAST CELL TUMORS 497
Administer diphenhydramine 1 mg/kg SQ prior to biopsy of suspected mast cell
tumor.
Use caution when obtaining a biopsy sample from a mast cell tumor; sites may bleed
excessively.
Canine grading systems:
Patnaik: based on cellularity, cell morphology, mitotic index, extent of tissue
involvement, and stromal reaction (survival greater than 1500 days reported):
Grade 1: well differentiated; located in the dermis and interfollicular spaces;
low potential for metastasis; (93%)
Grade 2: intermediate with rare mitotic figures; infiltrate to the deep dermis
and subcutaneous tissue; potential for local invasion and moderate poten-
tial for metastasis (47%)
Grade 3: undifferentiated or anaplastic with 3–6 mitotic figures; infiltrate
into/beyond subcutaneous tissue; high potential for metastasis (6%)
Kiupel: low grade or high grade:High grade: characterized by any one of these criteria (per 10 hpf):
◦At least 7 mitotic figures
◦At least 3 multinucleated cells
◦At least 3 bizarre nuclei
◦Karyomegaly
Median survival time greater than 2 years for low grade and less than 4
months for high grade.Cats: grading system not beneficial; no correlation between histopathologic appear-
ance of cutaneous tumor and prognosis.
Staging to determine the extent of disease and appropriate treatment:
Full physical exam
Bloodwork/urinalysis
Fine-needle aspirate of local lymph nodes even if they are not palpable
Abdominal ultrasound.
Additional tests to achieve complete staging: cytologic examination or biopsy of local
draining lymph node; cytologic examination of bone marrow aspirate is controversial;
thoracic radiography and abdominal ultrasonography.Negative clinical prognostic factors include advanced stage, caudal half of body loca-
tion, high tumor growth rate, aneuploidy, presence of systemic signs.
Negative molecular-based prognostic factors include increased AgNOR (silver nucle-
olar organizing regions), increased PCNA/Ki67 immunohistochemistry expression
(proliferation markers), increased vascularity and/or mitotic index, and increased c-
KIT expression; the use of these panels is strongly recommended due to significant
predictive ability for both development of metastasis and recurrence.THERAPEUTICS
Dogs
Aggressive surgical excision: treatment of choice.