15.3 Breast Staging (AJCC 8th Edition, Part XI): T, N, M, Anatomic & Prognostic Stage Groups
Key Takeaways
Breast T is based on the size of the largest invasive focus: T1mi 1 mm or less, T1a more than 1–5 mm, T1b more than 5–10 mm, T1c more than 10–20 mm, T2 more than 20–50 mm, and T3 more than 50 mm; tumors between 1 and 2 mm are rounded up to 2 mm.
T4 requires chest wall invasion (not pectoralis muscle alone), skin ulceration, macroscopic satellite skin nodules or edema including peau d'orange (T4b), both (T4c), or inflammatory carcinoma (T4d); dermal invasion alone is not T4.
LCIS was removed from the 8th edition T categories; Tis is DCIS or Paget disease without an underlying invasive or in situ tumor.
Isolated tumor cells (0.2 mm or less, or 200 cells or fewer) are pN0(i+), micrometastases (more than 0.2 mm to 2 mm) are pN1mi, and pN1a to pN3a count axillary nodes as 1–3, 4–9, and 10 or more.
U.S. registries record the prognostic stage groups, which add grade, ER, PR and HER2; a 21-gene recurrence score below 11 places T1–T2 N0 M0, ER-positive, HER2-negative tumors in pathological prognostic stage IA.
Primary tumor (T)
| T | Definition |
|---|---|
| TX | Primary tumor cannot be assessed |
| T0 | No evidence of primary tumor |
| Tis (DCIS) | Ductal carcinoma in situ |
| Tis (Paget) | Paget disease of the nipple not associated with invasive carcinoma or DCIS in the underlying parenchyma |
| T1mi | Invasive tumor 1 mm or less |
| T1a | More than 1 mm to 5 mm |
| T1b | More than 5 mm to 10 mm |
| T1c | More than 10 mm to 20 mm |
| T2 | More than 20 mm to 50 mm |
| T3 | More than 50 mm |
| T4a | Extension to the chest wall (ribs, intercostal muscles, serratus anterior). Invasion of the pectoralis muscle alone is not T4 |
| T4b | Skin ulceration, ipsilateral macroscopic satellite nodules, or skin edema (including peau d'orange) that does not meet inflammatory criteria |
| T4c | Both T4a and T4b |
| T4d | Inflammatory carcinoma |
T rules
- Measure the invasive component only. The DCIS portion does not add to T size.
- Rounding: round to the nearest millimeter. A tumor more than 1 mm but less than 2 mm is rounded up to 2 mm, so T1mi is only for 1.0 mm or less.
- Multiple tumors: T is based on the largest tumor, with the (m) suffix. Sizes of separate tumors are not added together.
- Dermal invasion alone, or skin dimpling or nipple retraction, does not make a tumor T4b. Ulceration, satellite nodules or edema are required.
- Inflammatory carcinoma (T4d) is a clinical diagnosis: diffuse erythema and edema involving a third or more of the breast skin. Tumor in dermal lymphatics without the clinical findings is not T4d.
- Paget disease with an underlying tumor is staged by the underlying tumor.
- LCIS is treated as a benign entity and was removed from the Tis categories in the 8th edition.
Regional lymph nodes (N)
Regional nodes: ipsilateral axillary nodes (levels I, II and III, including interpectoral or Rotter's nodes), ipsilateral internal mammary nodes, and ipsilateral supraclavicular nodes. Contralateral nodes and cervical nodes are distant (M1). Intramammary nodes are coded as axillary nodes.
Clinical N (cN)
| cN | Definition |
|---|---|
| cN1 | Movable ipsilateral level I or II axillary nodes |
| cN2a | Fixed or matted ipsilateral level I or II axillary nodes |
| cN2b | Ipsilateral internal mammary nodes without axillary nodes |
| cN3a | Ipsilateral infraclavicular (level III) nodes |
| cN3b | Ipsilateral internal mammary and axillary nodes |
| cN3c | Ipsilateral supraclavicular nodes |
Pathological N (pN)
| pN | Definition |
|---|---|
| pN0(i+) | Only isolated tumor cells (0.2 mm or less, or 200 cells or fewer) |
| pN1mi | Micrometastases: more than 0.2 mm (or more than 200 cells) but none larger than 2.0 mm |
| pN1a | 1–3 axillary nodes, at least one metastasis larger than 2.0 mm |
| pN1b | Ipsilateral internal mammary sentinel nodes, excluding ITCs |
| pN1c | pN1a plus pN1b |
| pN2a | 4–9 axillary nodes, at least one larger than 2.0 mm |
| pN2b | Clinically detected internal mammary nodes, with pathologically negative axillary nodes |
| pN3a | 10 or more axillary nodes, or infraclavicular (level III) nodes |
| pN3b | pN1a or pN2a with cN2b (imaging-positive internal mammary nodes), or pN2a with pN1b |
| pN3c | Ipsilateral supraclavicular nodes |
Node rules:
- Only nodes with metastases larger than 0.2 mm count toward the number of positive nodes. STORE applies the same rule to Regional Nodes Positive [820]: nodes with only ITCs are not counted as positive for any site except cutaneous melanoma and Merkel cell carcinoma. If the size of a nodal metastasis is not stated, assume it is larger than 0.2 mm.
- The (sn) suffix applies when only sentinel nodes were examined. The breast chapter drops (sn) when six or more sentinel nodes are removed.
Distant metastasis (M)
| M | Definition |
|---|---|
| cM0 | No clinical or imaging evidence |
| cM0(i+) | No clinical or imaging evidence, but tumor cells or deposits 0.2 mm or smaller found in blood, bone marrow or other non-regional tissue, without symptoms |
| cM1 | Distant metastasis by clinical or imaging means |
| pM1 | Histologically proven metastasis larger than 0.2 mm, or in non-regional nodes |
Anatomic stage groups
| Stage | T | N | M |
|---|---|---|---|
| 0 | Tis | N0 | M0 |
| IA | T1 | N0 | M0 |
| IB | T0–T1 | N1mi | M0 |
| IIA | T0–T1 | N1 | M0 |
| IIA | T2 | N0 | M0 |
| IIB | T2 | N1 | M0 |
| IIB | T3 | N0 | M0 |
| IIIA | T0–T3 | N2 | M0 |
| IIIA | T3 | N1 | M0 |
| IIIB | T4 | N0–N2 | M0 |
| IIIC | Any T | N3 | M0 |
| IV | Any T | Any N | M1 |
Prognostic stage groups
- The 8th edition added Clinical Prognostic Stage (for all patients) and Pathological Prognostic Stage (for patients whose first treatment is surgery). They combine anatomic TNM with grade, HER2, ER and PR. In the United States, these prognostic stage groups are used for patient care and registry reporting. The anatomic table is for regions where biomarker testing is not available.
- 21-gene recurrence score: for T1–T2, N0, M0, ER-positive, HER2-negative tumors, a score below 11 puts the pathological prognostic stage at IA, whatever the grade or PR status.
- Missing biomarkers can prevent a valid prognostic stage group. In STORE, a stage group that cannot be determined is coded 99.
- Tumors that are ER-, PR- and HER2-negative (triple negative) tend to move to a higher prognostic stage than their anatomic stage. Low-grade, ER-positive, HER2-positive tumors tend to move lower.
Post-neoadjuvant (yp) notes
- ypT is based on the largest contiguous focus of residual invasive tumor. Treatment-related fibrosis is excluded.
- ypN uses the same size thresholds. Nodes with treatment effect but no residual tumor are negative.
- A patient who was M1 before therapy stays stage IV after therapy.
Worked examples
- A 1.6 cm invasive carcinoma NST, 0 of 3 sentinel nodes, no clinical evidence of metastasis, is resected first. That gives pT1c pN0(sn) cM0, anatomic stage IA, and a prognostic stage that depends on grade, ER, PR and HER2.
- A 3.5 cm tumor with 4 of 14 axillary nodes positive (largest deposit 6 mm) gives pT2 pN2a cM0, anatomic stage IIIA.
- Peau d'orange over the lower half of the breast, a 2 cm underlying mass, and no diffuse erythema gives cT4b, not T4d, because inflammatory carcinoma needs its clinical criteria.
An invasive breast carcinoma measures 1.3 mm on the pathology report. What is the pathological T category?
pT1mi, because it is less than 2 mm
pT1a, because tumors larger than 1 mm and smaller than 2 mm are rounded up to 2 mm
pT1b, because it is more than 1 mm
pTis, because it is a microscopic focus
A sentinel node biopsy shows metastatic deposits of 1.5 mm in one node and isolated tumor cells in another. No other nodes were removed. What is the pN category?
pN0(i+)
pN1mi(sn)
pN1a(sn)
pN2a
A breast tumor invades the pectoralis major muscle but not the ribs, intercostal muscles or serratus anterior, and the skin is intact. How does this affect the T category?
It does not make the tumor T4; invasion of the pectoralis muscle alone is not chest wall invasion, so T is based on size.
It is T4b because the tumor is fixed.
It is T4a because the muscle is part of the chest wall.
It is T4d because the tumor is advanced.
Sections you finish are checked off in the contents.