Which of the following is NOT a principal part of the ICD-O code?

• A. Topography (primary site)
• B. Morphology (cell type)
• C. Behavior
• D. Grade

Answer: (D)

The main idea is that the ICD-O coding system is built from three essential parts: where the tumor started (topography or primary site), what the tumor is (morphology, which includes the histologic type and, with its behavior component, whether it’s benign, in situ, or malignant), and how the tumor behaves. Grade isn’t part of that coding structure. It’s a separate measure of how differentiated the cancer cells are and is often recorded for prognosis, but it isn’t encoded in the ICD-O code itself. So, you’d capture the site and the histology with a behavior tag in the morphology part, while grade would be noted separately outside the ICD-O code.