Page 1427 - Clinical Small Animal Internal Medicine

155 Mast Cell Neoplasia 1365

Adjuvant therapy with vinblastine/lomustine or Feline Mast Cell Tumors
VetBooks.ir Palladia for high‐grade MCT is recommended even if Epidemiology
the mass has been completely excised. Most adjuvant
treatment protocols strive for 3–6 months of therapy,
depending on tumor response and the patient’s toler- Feline MCTs represent the second most common skin
ance. In the adjuvant setting, chemotherapy results in tumor in the cat. A genetic correlation has been linked to
median overall survival times of 11–16 months. young Siamese cats. In addition, cats may develop both a
visceral form of MCT that primarily originates in the
spleen and a primary intestinal form.
Prognosis
Multiple factors have prognostic value for canine Signalment
MCTs. A subset of tumors have a more aggressive Cutaneous forms of feline MCTs are most commonly
behavior based on their anatomic location. MCTs found in cats 10 years of age, with no reported gender
of the inguinal region (groin, perivulvar, scrotal, predilection. Siamese less than 4 years of age are reported
perianal) have historically been regarded as having to be predisposed to the less common histiocytic form of
greater metastatic potential. Newer information has cutaneous MCT. Visceral (both spleen and intestinal
revealed that survival is dependent on histologic involvement) forms more commonly occur in older cats.
grade. However, dogs with MCTs in these locations,
specifically preputial and scrotal, have a decreased History and Clinical Signs
disease‐free interval as both local recurrence and the
development of subsequent MCTs are common. The The majority of cutaneous lesions occur on the head and
biologic behavior of tumors in these areas is still neck but can occur throughout the body. The most com-
debated so it is reasonable to use caution and proceed mon presentation is a red, raised dermal lesion. As in the
with routine MCT staging and more routine follow‐up canine form, MCTs can appear with many other cutane-
regardless of grade. ous manifestations including ulcerations, plaques, etc.
Mucocutaneous MCT (muzzle, vulva, sclera, etc.) and (Figure 155.6).
oral locations (tongue, palate) have a greater metastatic Both abdominal forms of MCT result in a systemically ill
potential regardless of grade and should be aggressively patient. Vomiting, lethargy, and weight loss are most com-
staged at the time of cytologic diagnosis. monly noted. Splenomegaly can be severe on abdominal
Mast cell tumors are the third most common tumor of palpation while an intestinal mass is not always detected.
the canine nailbed and have a more aggressive behavior
compared to a traditional cutaneous MCT. Finally, pri- Diagnosis
mary visceral mastocytosis should be considered a highly
aggressive neoplasm which is a terminal condition for Cytology is an appropriate diagnostic tool for both cuta-
most dogs. neous and visceral lesions. Because of the incidence of
As previously stated, histopathologic grading offers
the most accurate prognosis. The majority of grade I
(Patnaik) or low‐grade (Kiupel) tumors are cured with
complete excision. Less than 10% of grade I MCTs are
reported to metastasize, with a median survival time of
greater than two years. Alternatively, over 80% of grade
III MCTs will metastasize and the median survival for
high‐grade MCT is less than four months.
Various proliferation markers may be used for addi-
tional prognostic information. Dogs with a Ki‐67 index
of <1.8 had a median survival time that was not reached
within the time frame of the study and suggested a cura-
tive outcome. Those with a Ki‐67 >1.8 had a median sur-
vival time of 9.7 months. While increases in both
AgNORs and PCNA repeatedly support more aggressive
tumors, they appear to only be prognostically valuable in
conjunction with tumor grade. When evaluated inde- Figure 155.6 A clinically aggressive feline MCT. Note the change
pendently of grade, both indices are ineffective in deter- in coloration and ulceration throughout the lesion as well as the
mining prognosis. bruising at the base of the mass.