Exam 2 - Mast Cell Tumors Flashcards by Madeleine Swindell

what is the most common skin tumor in the dog?

mast cell - 16-21% of all skin tumors

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what breeds are predisposed to mast cell tumors?

brachycephalic breeds, labs, beagles, & schnauzers

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what is the average age of an animal affected by a mast cell tumor?

9 years old - but can be seen in dogs as young as 3 weeks old

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what are the 3 forms of mast cell tumors in dogs?

dermal form
visceral form
intestinal form

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what are the clinical signs of dermal mast cell tumors in dogs?

variable signs

release of bioactive constituents result in - gi ulcers, hypotension, coagulation abnormalities, & delayed wound healing

solitary vs. multiple masses

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what is darier’s sign?

local reaction seen when a mast cell tumor degranulates

urticaria, erythema, hives, & edema

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what is shown here?

dermal MCT showing darier’s sign - urticaria, edema, erythema, & hives

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where do MCT almost never metastasize to?

the lungs

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what are the common sites of metastasis of mast cell tumors?

lymph nodes, spleen, liver, & bone marrow

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what is the prognosis of a low grade mast cell tumor? what is the rate of metastasis seen?

MST > 2 years

<18% metastatic rate

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what is the prognosis of a high grade mast cell tumor? what is the rate of metastasis seen?

MST < 4 months

metastatic rate >70%

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what are the characteristics that signify a high grade mast cell tumor?

mitotic index >/= 7

> 3 multinucleate cells in 10 HPF

> 3 bizarre nuclei in 10 HPF

karyomegaly - abnormally enlarged cell nucleus, at least 10% of cells that have a 2 fold increase in size to qualify for this

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what is the 2 tier grading system of mast cell tumors? what does it apply to?

only applies to cutaneous MST - 96.8% consistency & 99.3% agreement

broken up into low grade (90% of tumors we see are considered to be low grade) & high grade

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using WHO staging, what is a stage 0 MCT?

1 tumor that is incompletely excised from the dermis, identified histologically without regional lymph node involvement

0a - no systemic signs
0b - systemic signs present

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using WHO staging, what is a stage I MCT?

1 tumor confined to the dermis without regional lymph node involvement

1a - no systemic signs
1b - systemic signs present

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using WHO staging, what is a stage II MCT?

1 tumor confined to the dermis with regional lymph node involvement

IIa - no systemic signs
IIb - systemic signs present

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using WHO staging, what is a stage III MCT?

multiple dermal tumors

large, infiltrating tumors with or without regional lymph node involvement

IIIa - no systemic signs
IIIb - systemic signs present

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using WHO staging, what is a stage IV MCT?

any tumor with distant metastasis including blood or bone marrow involvement

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how are cutaneous MCT diagnosed?

FNA - often bleed & swell

biopsy - pre-medicate the animal with benadryl, famotidine, +/- steroids to avoid side effects of histamine release

IHC

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what special stains are used for diagnosing MCT?

wright stain commonly used

t-blue, vimentin, a-1-antitrypsin, & CD117 (c-kit)

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what is the mast cell tumor prognostic panel? what is included?

a panel of factors known to help predict MCT behavior - has to be done on biopsied tissue

Ki67, AgNOR, c-kit (staining pattern & PCR for mutations)

c-kit - will tell you how much you have on the surface, but doesn’t tell you if it is mutated!!!!

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what staging is used for MCT?

bloodwork - cbc, chemistry, & UA

regional lymph node aspirates

chest rads

abdominal ultrasound

what are some prognostic factors evaluated for MCT?

histological grade - best predictor for dermal tumors!!!!!

clinical stage

location - mucocutaneous junctions are worse

cell proliferation

growth rate

recurrence - always will come back more aggressive than the first time

systemic signs - indicates more severe disease/stage

breed of the animal - boxers tend to get low grade MCT & labs tend to get high grade MCT

c-kit mutation - exxon 11 mutations have a worse prognosis vs no mutations or exxon 8 mutation

tumor size - bigger the tumor, the harder it is to get local control

how is surgery used to treat cutaneous MCT?

premedicate the animal - diphenhydramine & steroids

get 2-3cm margins & 1 fascial plane deep - look for enlarged lymph nodes

may use cytoreduction or amputation

when is radiation therapy used for cutaneous MCT?

only in microscopic disease!!!!!!!! worried about massive anaphylactic reaction due to mass degranulation of tumor, so used after surgery to clean up margins definitive therapy with 85-95% cure rate for grade I tumors & 50% 1 year control rate for grade III tumors

what long term radiation effects are seen in animals with cutaneous MCT?

depigmentation at most intense site of treatment, hyperpigmentation around the general area, alopecia, & hair changes colors in the areas that received the least amount of radiation

what chemo drug will you never use for an animal with cutaneous MCT? why?

doxorubicin - main side effect is mast cell degranulation causing a hypersensitivity like reaction

when is chemo used for MCT? what drugs can be used?

high grade tumors, microscopic setting after surgical removal, & non-resectable tumors vinblastine (blasts mast cells, #1 drug), lomustine, cyclophosphamide, & chlorambucil - use all concurrently with prednisone!!!! all drugs here are cytotoxic - will kill cells, always start with a cytotoxic drug

how does torceranib phosphate (palladia) work for treating cutaneous MCT? what are some side effects associated with it?

good class of drug for treating MCT with c-kit mutations - receptor tyrosine kinase inhibitor that inhibits VEGF, PDGFR, c-kit, & FGFR gi ulcers, muscle pain, neutropenia, thrombocytopenia, & proteinuria

how does masitinib mesylate (kinavet) work for treating cutaneous MCT? what are some side effects associated with it?

receptor tyrosine kinase inhibitor that inhibits PDGFR, c-kit, & mutated FGFR gi ulceration, neutropenia, & proteinuria

what are some treatment options for ancillary therapy for a patient with MCT?

diphenhydramine, h-2 blockers, sucralfate, pain meds, & protamine

what is the MST for intestinal mast cell tumors in dogs & cats with aggressive therapy? why?

<120 days - very aggressive tumor type with a very high metastatic rate

what treatment is recommended for intestinal mast cell tumors in dogs & cats?

surgical removal with 10cm margins & always followed with chemotherapy

what is the visceral form of MCT in cats?

spleen, liver, lymph nodes, & bone marrow are involved

what is the cutaneous form of MCT in cats?

of the dermis - head & neck, non-haired areas, fleshy, & often in multiples

what cat breed/signalment is predisposed to cutaneous MCT?

young male siamese cats

what is the 2nd most common skin tumor in cats?

cutaneous mast cell tumor - makes up 20% of all skin tumors

what is the typical age of a cat seen with a mastocytic cutaneous MCT?

10 years old - similar to MCT found in dogs

what is the typical age of a cat seen with a histiocytic cutaneous MCT?

young cats - 2.4 years old, histiocytic mast cells that act like histiocytomas in dogs, look like eosinophilic plaques need to do a biopsy to differentiate mast cell tumor from rodent ulcer

T/F: cats rarely show systemic signs with cutaneous MCT

true

what are some clinical signs associated with visceral MCT in cats?

weight loss, anorexia, diarrhea, melena, vomiting, collapse, & death

what clinical signs are seen with cutaneous MCT in cats?

rare to see systemic signs - usually a lesion noticed by the owner that may be ulcerated

how are MCT diagnosed in cats?

FNA or biopsy pre-medicate if aspirating the spleen - full of MAST CELLS!!!!!

how are MCT staged in cats?

CBC/chemistry/UA FNA of regional lymph nodes chest rads & abdominal ultrasound

what is the treatment used for cutaneous MCT in cats?

surgery - narrow margins are necessary benign neglect - tumors often regress

what is the MST of visceral MCT in cats treated with splenectomy/surgery?

11-24 months

is chemotherapy used in cats with visceral MCT? what drugs?

it is but it is untested - used prednisolone, diphenhydramine, famotidine & watch it vinblastine, lomustine, & chlorambucil

T/F: there is no worked out grading system for any type of MCT apart from dermal MCT

true - no grading established for tumors in the SQ

what organs are most commonly implicated in the visceral form of MCT?

liver & spleen

what is the only form of MCT that is the same in dogs & cats?

intestinal MCT

T/F: if CD117 is negative, it is not a mast cell tumor

true - all MCT will stain with CD117

what kind of receptors are tyrosine kinase? why are they a good target for drug therapy?

growth factor receptors 95% of protein interactions in the cell will not be affected by the inhibitor

instead of grading in cutaneous MCT in cats, what is provided instead?

whether the tumor is compact vs. diffuse compact - lower grade, well circumscribed diffuse - infiltrative, higher grade

why is a splenectomy done for a cat with visceral MCT?

every time the animal jumps/is picked up/squeezed - the mass degranulates further exacerbating clinical signs