Mast Cell Tumors Flashcards
What is the most common skin tumor of dogs?
Mast cell tumors
What is a MCT nickname?
The Great Pretender
Why do MCTs often fluctuate in size
Degranulation
What do mast cell tumors contain?
Histamine, heparin, eosinophilic chemotactic factor, proteases
How do MCTs cause GI ulcers?
H2 receptor activation
Grading applies to which MCTs?
Dermal MCTs only
How do you grade an MCT?
Histopathology
What is the most common MCT grading scheme?
Patnaik
Well differentiated, low mitotic index, small and superficial in dermis
Grade 1 MCT
Low likelihood for recurrence and mets after removal
Grade 1 MCT
Moderately differentiated, low/mod mitotic index, mild/mod invasive
Grade 2 MCT
Low to moderate likelihood for recurrence and mets after removal
Grade 2 MCT
High likelihood for recurrence and mets after removal
Grade 3 MCT
Poorly differentiated, high mitotic index, invasive
Grade 3 MCT
What is considered a high mitotic index?
5+ mitoses/10hpf
Which grade of MCTs are most common (80%)
Grade 2
What will a MCT look like on FNA cytology?
Individual round cells w/dark granules in cytoplasm and background
What other WBC is commonly seen with MCTs?
Eosinophils
How do you stage an MCT?
LN aspirate, abd ultrasound, thoracic rads
Which LN should be aspirated to stage an MCT?
Dependent draining LN (not necessarily the closest one)
What margins do you want to get for MCTs w/o mets?
2-3cm lateral margins + 1 fascial plane deep
When is chemo indicated for MCTs?
Grade 3/high grade 2 tumors, if mets are present, unresectable tumors
Which chemo agents are commonly used to treat MCTs?
Vinblastine, CCNU, Palladia, Pred
What gene mutation is commonly found in aggressive MCTs?
c-kit
Which chemo drugs target the mutated c-kit gene found in MCTs?
Tyrosine kinase inhibitors (Palladia, Kinavet)
What are supportive treatments used to minimize histamine degranulation?
H1 and H2 blockers
Is having multiple dermal MCTs considered a negative prognostic indicator?
No - each tumor is treated individually
Which dog breeds frequently develop multiple MCTs over their lifetime but are usually assoc. w/lower grade tumors?
Brachycephalics
What do mast cell granules release?
Histamine, heparin, proteases, cytokines
Can MCT grade be determined with cytology?
No
What margins do you want when excising an MCT?
2-3cm lateral + 1 facial plane deep
What chemotherapy is indicated for MCTs?
Vinblastine, CCNU or other alkylating agents
How does prednisone support a MCT dog?
Cytotoxic to mast cells, reduces inflammation within the tumor
What H1 blocker (histamine) can you give to relieve consequences of mast cell degranulation?
Diphenhydramine
What H2 blocker (histamine) can you give to relieve consequences of mast cell degranulation?
Famotidine, ranitidine
What is the first FDA-approved drug for canine cancer in the US?
Palladia (Toceranib)
What is the MoA of Palladia (Toceranib)?
Inhibits aberrant cell signaling pathways found in MCTs (tyrosine kinase inhibitor)
What are proliferation markers of MCTs used as prognostic indicators?
Ki-67, PCNA, AgNOR
Dogs with which gene mutation assoc. w/MCTs have a worse prognosis?
c-KIT mutation
