Page 1428 - Clinical Small Animal Internal Medicine

1366 Section 11 Oncologic Disease

visceral mastocytosis associated with splenomegaly, the The visceral form is rarely cured with splenectomy so
VetBooks.ir author strongly suggests the use of systemic antihista- adjuvant treatment is recommended. Currently, there is
no one accepted standard chemotherapy protocol for
mines prior to cytology of an enlarged spleen. It is equally
important to have corticosteroids readily available in
2
at a dose of 50–60 mg/m (author’s note: 10 mg/cat
case the cytology procedure results in an acute anaphy- use in cats. Single‐agent lomustine has been evaluated
lactic reaction. It is not necessary to premedicate all is considered an acceptable lomustine dose) with a
cats prior to cytology of an intestinal lesion. However, reported overall response rate of 50%, with neutropenia
evidence of mast cells on the cytology sample justifies and thrombocytopenia the most common and signifi-
administration of antihistamines at that time. cant toxicities. Due to the variation in clinical picture,
An abdominal ultrasound is recommended for visceral accurate survival times have not yet been determined.
mastocytosis. Additionally, mastocytemia is often noted Sixty‐seven percent of feline MCTs are noted to have a
on routine complete blood counts and can be isolated c‐kit mutation. At the time of publication, there are no
within the buffy coat. published clinical data on the efficacy of tyrosine kinase
Due to the low risk of metastasis, routine presurgical inhibitors against feline MCTs. Masitinib has been eval-
staging for skin tumors may not be indicated unless the uated in cats in a Phase I trial. The results indicate the
patient has a clinical presentation (rapidly growing drug is well tolerated at 12.5 mg/kg once a day with pro-
tumor) that supports a more aggressive phenotype. teinuria noted as the most significant side‐effect. Based
However, visceral and intestinal MCT should undergo on the tolerability of the medication and the proven c‐kit
complete staging with abdominal ultrasound, cytology mutation, use of tyrosine kinase inhibitor therapy in
of the liver and spleen, thoracic radiographs, minimum felines, in similar clinical situations as described in
database bloodwork, buffy coat and potentially bone canines, appears reasonable.
marrow aspiration. If possible, intestinal resection with 5–10 cm margins
should be considered for patients with the intestinal
form. Unlike the splenic form, the presence of metastasis
Therapy
is much more clinically relevant as it will alter the prog-
Cutaneous lesions that are <1 cm in diameter can be nosis significantly.
removed with routine excision. As their behavior is dif-
ferent from that of canine MCT, surgical margins of Prognosis
2 cm are not indicated in cats. Routine “lumpectomy”
or excisional biopsy margins are appropriate. If a mini- Neither the Patnaik nor Kiupel grading scheme is appro-
mal surgery is attempted, it is important to allow room priate for feline cutaneous tumors. MCTs are labeled as
for a second, wider surgery, should histopathology indi- either the more common mastocytic form or the histio-
cate a more aggressive lesion. For the clinically low‐ cytic form. The latter type is often found in juvenile
grade (dermal, <1 cm) tumors, local plesiotherapy with Siamese cats. The mastocytic form is then subtyped into
strontium‐90 radiation probes offers the same curative either compact or diffuse. Compact mastocytic (more
outcome and can be used in areas where routine commonly referred to as well‐differentiated) MCT rep-
removal is unattainable. resents 50–90% of all cutaneous MCTs in cats. The
Both intestinal and splenic (or true visceral) mastocy- behavior of these lesions is benign and excisional biopsy
tosis require abdominal exploratory surgery. Systemic may be all that is required for the majority of patients.
therapy with antihistamines and corticosteroids is The diffuse mastocytic form has a behavior similar to
rarely effective at resolving clinical signs. Splenectomy canine MCT. Thus, additional wide surgical margins and
is the treatment of choice for cats with the splenic form. routine staging are indicated.
Within reason, this procedure is still clinically applica- Splenectomy as a single treatment modality for the vis-
ble in the face of mild to moderate distant metastasis as ceral form will result in a median survival time of 12–18
splenectomy results in significant reduction in tumor months. As previously stated, evidence of metastasis in
burden and histamine release. However, splenectomy other organs (lungs, liver, etc.) does not eliminate splenec-
itself can be a life‐threatening procedure due to the tomy as a surgical option due to the significant reduction
massive histamine release caused during splenic manip- in tumor burden and resulting improved clinical outcome.
ulation. It is recommended to premedicate all cats with However, in the face of severe multifocal disease, splenec-
appropriate dosing of diphenhydramine, famotidine, tomy alone should not be considered.
and dexamethasone preoperatively. Additionally, the The primary intestinal form historically caried the
spleen should be handled gently during vascular liga- most guarded prognosis (4–6 weeks survival). However,
tion and gently lifted out of the abdomen via a generous more recent studies indicate that the prognosis may be
abdominal incision. far better (median survival time 531 days).