In Patnaik grading, which grade shows 3–6 mitotic figures per HPF?

• A. Grade II
• B. Grade IV
• C. Grade III
• D. Grade I

Answer: (C)

Patnaik grading for canine mast cell tumors links tumor differentiation with mitotic activity to classify aggressiveness. A higher number of mitotic figures per high-power field signals a more aggressive tumor. In this system, a mitotic rate of 3–6 per HPF reflects a high mitotic index and fits the poorly differentiated, Grade III category. Grade I is well differentiated with few mitotic figures, and Grade II is intermediate with variable mitotic activity. Therefore, this range corresponds to the most aggressive grade, guiding prognosis and treatment. (Note: some sources count per 10 HPF or use slightly different thresholds, but in Patnaik grading this mitotic range aligns with the high-grade category.)