Grading Cutaneous Mast Cell Tumors in Cats.

Area of Science:

• Veterinary Oncology
• Comparative Pathology

Background:

• Cutaneous mast cell tumors (cMCTs) represent approximately 20% of feline skin neoplasms.
• Prognosis for feline cMCTs is challenging due to the absence of a standardized grading system.
• While often benign, some feline cMCTs exhibit aggressive behavior, leading to metastasis or disseminated disease.

Purpose of the Study:

• To develop and evaluate a novel grading scheme for feline cutaneous mast cell tumors.
• To identify macroscopic and histologic criteria that differentiate between aggressive and non-aggressive cMCTs in cats.
• To improve prognostic accuracy for feline cMCTs.

Main Methods:

• Retrospective evaluation of macroscopic and histologic features in feline cMCT cases treated with surgery.
• Classification of cats into two groups based on clinical outcome at 1000 days post-surgery (disease-free vs. metastatic/disseminated disease).
• Development of a grading scheme based on mitotic figures, tumor diameter, nuclear shape, and nucleolar characteristics.

Main Results:

• A grading scheme was developed, classifying tumors as high-grade (>5 mitotic figures, >1.5 cm diameter, irregular nuclear shape, or prominent nucleoli/chromatin clusters).
• High-grade feline cMCTs (24% of cases) had a significantly shorter median survival time (349 days) compared to low-grade tumors (median not reached).
• The grading system showed significant differentiation between the two outcome groups (P < .001).

Conclusions:

• The proposed grading system effectively differentiates feline cMCTs with different clinical outcomes.
• This new grading scheme offers a valuable tool for estimating prognosis in cats with cutaneous mast cell tumors.
• Further validation on larger case series is recommended to confirm reproducibility and clinical utility.