15.1 AJCC TNM Principles: Categories, Prefixes, Suffixes, General Rules & Registry Items
Key Takeaways
T describes the primary tumor, N the regional lymph nodes and M distant metastasis; TX and NX mean they cannot be assessed, and MX is no longer a valid category.
When there is doubt between two categories, AJCC's general rule is to assign the lower, less advanced category.
Prefixes identify the classification: c clinical, p pathological, yc and yp after neoadjuvant therapy, r recurrence or retreatment, and a autopsy; suffixes include (m) for multiple tumors, (sn) sentinel node, (f) FNA or core biopsy, and (i+) or (mol+) for isolated tumor cells.
pM0 is not used except at autopsy; if distant metastasis is not proven microscopically, pathological staging uses cM0, and microscopic confirmation of metastasis gives pM1 in either time frame.
STORE requires AJCC TNM items for Class of Case 10–22; code 88 is only for site and histology combinations or in situ tumors that AJCC does not stage, and 99 is for a stage group that cannot be determined.
Why TNM
AJCC staging gives physicians and registries a shared language for prognosis, treatment planning and outcome comparison. CoC requires accredited programs to record AJCC staging using the edition in effect for the diagnosis year. That is the AJCC Cancer Staging Manual, 8th edition for 2018 and later, plus Version 9 chapters as AJCC releases them for individual sites. For example, cervix Version 9 applies to 2021 and later diagnoses, and lung Version 9 to 2025 and later (Section 15.4).
The three categories
| Category | Describes | Typical values |
|---|---|---|
| T | Primary tumor size and extension | TX (cannot be assessed), T0 (no evidence of primary), Tis (in situ), T1–T4 with subcategories |
| N | Regional lymph nodes | NX (cannot be assessed), N0, N1–N3 with subcategories |
| M | Distant metastasis | cM0, cM1 (clinical evidence), pM1 (microscopically confirmed), with subcategories such as M1a–M1c |
- MX is not used. It was eliminated in the 7th edition. If there is no clinical evidence of distant metastasis, the category is cM0.
- Each chapter defines its own regional lymph nodes. Nodes that are not regional count as M disease. For example, contralateral axillary nodes in breast cancer are M1.
- Direct extension of the primary tumor into a regional node counts as node involvement.
General rules
- Uncertainty rule: if it is unclear which of two categories applies, assign the lower (less advanced) category. The same applies to stage groups.
- Multiple synchronous tumors in one organ: assign T from the tumor with the highest T, and show multiplicity with (m) or the number of tumors, for example T2(m) or T2(3). Some chapters, such as thyroid and lung, have their own multiplicity rules.
- Tumor size: use the chapter's rounding rules. Most chapters round to the nearest millimeter. For example, a breast tumor measuring 1.2 mm is rounded to 2 mm, so it is not T1mi.
- Stage groups combine T, N and M, and in some chapters also prognostic factors:
- grade, ER, PR, HER2 and multigene scores for breast;
- PSA and Grade Group for prostate;
- serum markers (S) for testis;
- grade for some other sites.
- All information in the time frame is used, including information from other facilities.
Prefixes
| Prefix | Classification |
|---|---|
| c | Clinical: before treatment (Section 15.2) |
| p | Pathological: clinical information plus surgical resection findings, with no neoadjuvant therapy |
| yc | Post-therapy clinical: after neoadjuvant therapy or primary systemic or radiation therapy, before surgery |
| yp | Post-therapy pathological: surgery after neoadjuvant therapy |
| r | Recurrence or retreatment staging. It does not replace the original stage in the registry |
| a | Autopsy: cancer first found at autopsy |
Suffixes and descriptors
| Descriptor | Meaning |
|---|---|
| (m) | Multiple primary tumors in one site |
| (sn) | N assessed by sentinel node biopsy only, for example pN1(sn) |
| (f) | N assessed by FNA or core needle biopsy only, for example cN1(f) |
| (i+) | Isolated tumor cells: 0.2 mm or smaller, or 200 cells or fewer in breast. In most chapters ITCs are categorized as N0(i+) |
| (mol+) | Tumor detected only by molecular methods |
Pathological classification without a complete resection
- pT usually needs resection of the primary tumor. Microscopic confirmation of the highest T category (for example, a biopsy showing invasion of an adjacent organ that makes the tumor T4) can support pT.
- pN needs removal of nodes adequate to show the N category. Microscopic confirmation of a node in the highest N category (for example, a biopsy of a node that defines N3) is enough for pN.
- pM1 means distant metastasis is microscopically confirmed. If pM1 is proven during the clinical time frame, the case can be assigned stage IV in both the clinical and pathological classifications.
- pM0 is not used, except at autopsy. When a resection shows no distant disease and none was proven microscopically, the pathological classification uses cM0.
STORE registry items
| Classification | T | N | M | Stage group |
|---|---|---|---|---|
| Clinical | 1001 | 1002 | 1003 | 1004 |
| Pathological | 1011 | 1012 | 1013 | 1014 |
| Post-therapy pathological (yp) | 1021 | 1022 | 1023 | 1024 |
| Post-therapy clinical (yc), 2021+ | 1062 onward |
STORE rules:
- The clinical and pathological T, N and M items must be assigned for Class of Case 10–22. Clinical M is strongly recommended for Class 00 when the workup allows.
- Record the stage the managing physician documents. If none is recorded, the registrar assigns it from the best available information, without needing to contact the physician.
- Code 88 is for a site and histology combination not defined in the current AJCC edition, and for in situ tumors that AJCC does not stage. It is not a general "not applicable" code for a classification whose criteria were not met.
- Code 99 is for a stage group when the TNM combination, together with any required prognostic factors, does not produce a valid stage group.
- Values are left-justified in 15-character fields, using AJCC's published code labels (for example, "cT2a").
Worked example
A 2.4 cm invasive breast carcinoma with a positive sentinel node (macrometastasis 3 mm, 1 of 2 nodes) and no distant work-up findings is resected without neoadjuvant therapy. The result is pT2 pN1a(sn) cM0. The pathological M category is cM0, not pM0. The prognostic stage group then depends on grade, ER, PR and HER2 (Section 15.3).
A colon resection shows pT3 pN1a. Imaging before surgery showed no distant metastasis, and no metastatic site was biopsied. How is the M category recorded for pathological staging?
pM0
MX
cM0
M category is left unknown, so the stage group is 99
A radiologist describes a lung mass as "4.0 to 4.5 cm." The physician does not specify further, and the choice affects the T category (T2a versus T2b). Which general AJCC rule applies?
Use the larger measurement to avoid understaging.
Average the two measurements.
When in doubt, assign the lower (less advanced) category.
Code TX because the size is uncertain.
According to STORE, when is code 88 used in the AJCC TNM items?
When the patient received neoadjuvant therapy, so pathological TNM does not apply
When the patient refused surgery
When the stage is unknown because the workup was incomplete
When the site and histology combination is not defined in the current AJCC edition, or for in situ tumors that AJCC does not stage
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