Page 1423 - Clinical Small Animal Internal Medicine

155 Mast Cell Neoplasia 1361

VetBooks.ir Box 155.1 Staging for mast cell tumors Stage 4: Any MCT with confirmed distant metastasis
WHO clinical staging system for canine mast cell tumors
Stage 0: Microscopic incomplete excision of any dermal MCT Modified WHO clinical staging criteria for canine mast
with no evidence of regional nodal or distant metastasis
Stage 1: A single MCT confined to the dermis with no evi- cell tumors
dence of regional nodal or distant metastasis Stage –1: Single MCT completely removed and no evidence
of regional nodal metastasis
a) no clinical signs Stage 0: Microscopic incomplete excision of a single MCT
b) clinical signs
with no evidence of regional nodal metastasis
Stage 2: A single MCT confined to the dermis with regional Stage 1: A single MCT completely removed
lymph node metastasis Stage 2: Microscopic incomplete excision of a single MCT
Stage 3: A single MCT completely removed with positive
a) no clinical signs regional node metastasis in situ
b) clinical signs
Stage 4: Microscopic incomplete excision of a single MCT
Stage 3: Multiple dermal MCT, any tumor invading local tis- with positive regional node metastasis in situ
sue with or without regional nodal metastasis Stage 5: MCT recurrence or positive distant metastasis
a) no clinical signs
b) clinical signs

liver and spleen does not influence treatment or survival The Patnaik grading scheme is the most well known
estimates. and used in pathology reports. Tumors are divided into
While historically pursued, bone marrow aspiration three grades (I, II, and III). Grade I tumors have an indo-
for staging may no longer be indicated for a patient diag- lent behavior with a metastatic potential of near 10%.
nosed with their first MCT or with no clinical evidence Grade III MCTs are exceptionally aggressive with a met-
of lymph node metastasis. For these dogs, the incidence astatic rate of 80%. Grade II MCTs are by far the most
of bone marrow involvement is low (2.8%). This low common diagnosis. These tumors can behave similarly
yield, combined with cost, invasiveness of the procedure, to both grade I and III and have a metastatic potential
and ability to prove distant metastasis on more routine near 20%. Clinically, this grading scheme is very helpful
testing (abdominal ultrasound), suggests that bone mar- for grade I and III lesions, but less predictive for grade II
row aspiration may not be necessary for every patient. tumors.
However, bone marrow metastasis/distant metastasis is As the vast majority of MCTs are in the grade II
a significant prognostic indicator and dogs with a recur- category, many clinicians struggle with interpretation
rent MCT or which develop subsequent MCTs may have and prognosis. Consequently, a recent collaboration of
a higher incidence (18.7%). pathologists and oncologists proposed a new grading
Pulmonary metastasis is rare and sporadically reported scheme. Kiupel et al. offered a two‐tiered system com-
for MCT. Consequently, thoracic radiography is not con- posed of a low‐grade and high‐grade MCT. First, this
sidered part of routine staging but may be helpful in study found an improved interpathologist agreement
assessing concomitant disease processes (cardiovascular, compared to the Patnaik scheme. Second, distinction
respiratory, etc.). between the two grades is based on a scoring system that
The most important prognostic indicator is the grad- evaluates mitotic index, karyomegaly, multinucleated
ing scheme. Tumor grade is determined by histopatho- cells, and bizarre nuclei. It is imperative to always request
logic features. Incisional biopsy is rarely recommended a microscopic description with mast cell histopathology
for a MCT due to the diagnostic capability of cytology as these characteristics are evaluated by that grading
and the increased potential for wound dehiscence sec- scheme. Low‐grade MCTs (the majority of previously
ondary to both histamine and heparin release from the diagnosed grade I and IIs) have minimal metastatic
remaining tumor cells. If cytology is nondiagnostic, inci- potential and a median survival time of greater than two
sional biopsy should be minimal in size and in an area of years. High‐grade MCTs have a median survival time of
minimal inflammation or necrosis. The incisional site less than four months due to the metastatic behavior of
should be easily excised in its entirety when the mass is these tumors. To further aid clinical decisions, many
removed. Overall, excisional biopsy is superior for both diagnostic labs have started to report both grading sys-
diagnostic and therapeutic purposes. tems in their histopathology reports.