In the TNM staging system, what does M1 designate?

Correct answer: D. Distant metastasis is present

• A. PRIMARY TUMOUR SIZE is the T category. For oral cancer, T1 is 2 cm or less, T2 is 2–4 cm, T3 exceeds 4 cm, and T4 indicates invasion of adjacent structures such as bone, deep muscle or skin.
• B. REGIONAL LYMPH NODE involvement is described by the N category (N0 through N3), not M.
• C. Invasion of adjacent structures is T4 — again a T descriptor, not M.
• D. CORRECT. In TNM, M describes DISTANT METASTASIS: M0 means no distant metastasis and M1 means distant metastasis IS present. The presence of M1 disease automatically places the patient at STAGE IV regardless of how small the primary tumour is or how few nodes are involved — it is the single most powerful determinant of prognosis.

Note: There is NO M2, M3 or M4 in the standard TNM system — the M category is only M0 or M1 (occasionally MX where it cannot be assessed). If you see this option set on the exam, M1 is the only defensible answer. T and N are subdivided numerically; M is essentially binary.