What is the major limitation of the Patnaik grading scheme?

• A. It is expensive to perform
• B. The majority of MCTs fall into Grade II, making behavior difficult to predict
• C. It is not used in dogs older than 8 years
• D. It only works for subcutaneous tumors

Answer: (B)

The key idea is that grading canine mast cell tumors with the Patnaik system often fails to reliably predict behavior. This system assigns tumors to three grades, but the majority of tumors fall into Grade II. That Category is a heterogeneous mix of tumors with widely different biologic courses—some behave indolently, others behave aggressively. Because of this, the histologic grade loses its prognostic usefulness: knowing a tumor is Grade II doesn’t tell you much about its likely future behavior or how aggressively to treat it. In contrast, clearly distinguishing tumors as strongly favorable (Grade I) or strongly aggressive (Grade III) is more informative, so the real limitation is the unpredictability within the Grade II group. This is why clinicians often seek additional prognostic factors or use newer, two-tier grading schemes to improve predictive accuracy.