Grading of Canine Mast Cell Tumors

Low Grade Mast Cell Tumors (Grade I)
•Cell round and monomorphic 
•Cells measure 10-12 microns in diameter 
•Nuclei small, hyperchromatic; inconspicuous nucleoli 
•Cytoplasm ample, distinct cell borders, intracytoplasmic granules 
•No mitoses 
•Confined to dermis and interfollicular spaces 
•Arranged in rows or small nests seperated by mature dermal collagen bundles 
•Minimal edema and necrosis in traumatized tumors 
•Time between detection and removal >28 weeks 
•Slow growing tumors 

Intermediate Grade Mast Cell Tumors (Grade II)
•Cell round to ovoid, occasional spindle cells and giant cells 
•Cells measure 12-15 microns in diameter, moderate pleomorphism 
•Nuclei are larger (8-10 microns), round or indented, scattered chromatin, single nucleoli 
•Binucleate cells 
•Cytoplasm distinct or indistinct, +/- intracytoplasmic granules 
•Rare mitoses 
•Infiltrate or replace lower dermal and subcutaneous tissue 
•Arranged in cords or nests with thin fibrovasular stroma 
•Stoma may be thick and fibrocollagenous with areas of hyalinization 
•Areas of diffuse edema and necrosis 
•Time between detection and removal <28 wekks 
•Rapidly growing tumors 

High Grade Mast Cell Tumors (Grade III)
•Cells are pleomorphic, round, ovoid, spindle cells 
•Cells measure 10-18 microns in diameter 
•Nuclei pleomorphic, often eccentric. Vesicular, indented, one or more prominent nucleoli 
•Binucleate, multinucleate or giant nuclei 
•Cytoplasm variable in amount +/- intracytoplasmic granules 
•Mitoses common 
•Infiltrate and replace subcutaneous and deeper tissues 
•Arranged in closely packed sheets 
•Stroma fibrovascular or fibrocellular with areas of hyalinization 
•Edema, hemorrhage and necrosis common 
•Time between detection and removal <28 weeks 
•Rapidly growing tumors 

Copyright © 2000 - University of Pennsylvania School of Veterinary Medicine
Faculty: Michael H. Goldschmidt, BVMS & Patricia Mcmanus,VMD, PhD
Student: Kyle Goldschmidt