Oncology · 7 min read
How cancer staging works: TNM explained
T describes the primary tumour, N the regional lymph nodes and M distant metastasis. Understanding what each letter means makes treatment discussions far easier to follow.
The TNM system, maintained by the UICC and AJCC, is the most widely used framework for describing how far a solid tumour has spread. T is graded from Tis (carcinoma in situ) through T1 to T4 by size or local invasion, N from N0 to N3 by the number and location of involved regional lymph nodes, and M as either M0 or M1 depending on whether distant metastasis is identified.
Clinical stage, written with a c prefix (for example cT2 N1 M0), is assigned before treatment using examination and imaging. Pathological stage, written with a p prefix, is assigned after surgical resection when the specimen has been examined histologically. The two do not always agree, and a change between them is a common reason patients seek a second opinion.
Stage alone does not determine treatment. Tumour grade, receptor and biomarker status, performance status and comorbidity all influence what is offered. This is why the same stage can lead to different recommendations in two different patients.