Which component is NOT part of the TNM cancer staging system?

• A. T (tumor size/extent)
• B. N (nodal involvement)
• C. M (metastasis)
• D. Histologic grade

Answer: (D)

TNM staging is based on three elements: the primary tumor (size and extent), regional lymph node involvement, and distant metastasis. These three components form the core coding used to describe how far cancer has spread.

The option describing histologic grade is not part of the TNM codes. Histologic grade, which indicates how differentiated the tumor cells look and how aggressively they may behave, is a separate descriptor (often noted as G) that provides prognostic information alongside the TNM stage. In practice, you might see a report labeled with a TNM code like T2N1M0 and an accompanying grade such as G2. But the TNM system itself does not include histologic grade.