Question 1

How do I select the correct T, N, and M categories?

Accepted Answer

T category is based on tumour size, depth of invasion, and extension to adjacent structures per the specific cancer schema. N category depends on number, size, and location of involved nodes. M category is binary (M0 = no distant metastases, M1 = present).

Question 2

Can the same TNM combination map to different stage groups across cancers?

Accepted Answer

Yes — each cancer has its own stage group table. For example, T2N0M0 is Stage I in colorectal cancer but Stage II in non-small cell lung cancer. Always use the cancer-specific schema.

Question 3

What edition of TNM should I use?

Accepted Answer

AJCC 8th Edition (2017) is the current standard for most cancers. Some cancer types have organ-specific editions or alternative classifications (e.g., WHO classification for CNS tumours).

Question 4

How is pathological TNM (pTNM) different from clinical TNM (cTNM)?

Accepted Answer

cTNM is based on clinical examination and imaging before treatment. pTNM is based on pathological examination of the surgical specimen. pTNM provides the most accurate prognostic information but is only available post-operatively.