Keynote Message

Histological grade remains the cornerstone for determining prognosis in canine cutaneous mast cell tumors (MCTs), however has not been without its challenges diagnostically and clinically, when biological behavior does not follow the anticipated clinical course. In an attempt to improve diagnostic accuracy of grade as well as predictability of prognosis, a new grading scheme was proposed in 2011. A number of studies followed implementing this scheme, which proved improvement in some areas but continued limitations in others. In April 2017, based on critical review of the literature, the VCS/ACVP Oncology-Pathology Working Group put forth a consensus ultimately suggesting the two schemes may be complementary and proposed a combined grading system. It is recognized that even this method cannot be considered foolproof but may provide improved accuracy/predictability or at least harness a better understanding of the potential biological behavior of the tumor in question. Additionally, grade should not be considered as a stand-alone prognostic factor but instead considered in conjunction with the overall clinical picture as well as with proliferation and molecular markers (e.g., mitoses, Ki67, KIT, c-kit) when possible.

Key References

1.  Patnaik AK, Ehler WJ, MacEwen EG. Canine cutaneous mast cell tumor: morphologic grading and survival time in 83 dogs. Vet Pathol. 1984;21:469–474.

2.  Kiupel M, Webster JD, Bailey KL, et al. Proposal of a 2-tier histologic grading system for canine cutaneous mast cell tumors to more accurately predict biological behavior. Vet Pathol. 2011;48:147–155. DOI: 10.1177/0300985810386469.

3.  Sabattini S, Scarpa F, Berlato D, Bettini G. Histologic grading of canine mast cell tumor: is 2 better than 3? Vet Pathol. 2014;52:70–73. DOI:10.1177/0300985814521638.

4.  Stefanello D, Buracco P, Sabattini S, et al. Comparison of 2- and 3-category histologic grading systems for predicting the presence of metastasis at the time of initial evaluation in dogs with cutaneous mast cell tumors: 386 cases (2009–2014). J Am Vet Med Assoc. 2015;246:765–769. DOI: 10.2460/javma.246.7.765.

5.  VCS/ACVP OPWG Updated Consensus on Grading of Canine Cutaneous Mast Cell Tumors.
http://vetcancersociety.org/vcs-members/vcs-groups/oncology-pathology-working-group/ (VIN editor: the original link was modified on 7/28/2017).