Breast Cancer Staging
TNM Overview
Staging uses the AJCC 8th edition TNM system, which now incorporates tumor grade, tumor biomarkers, and multigene panel (e.g., Oncotype Dx) in addition to anatomic stage.
Tumor Size (T)
| Stage | Criteria |
|---|---|
| Tis | DCIS, Paget disease without underlying DCIS/invasive cancer |
| T1 | ≤ 2 cm (longest dimension) |
| T1mi | Microscopic invasion < 1 mm |
| T2 | 21–50 mm |
| T3 | > 5 cm |
| T4 | Skin or chest wall involvement (any size) |
T4 subcategories:
- T4a — Chest wall involvement (intercostals, ribs, serratus anterior; NOT pectoralis)
- T4b — Skin ulceration, skin nodules, edema (separate from primary tumor)
- T4c — T4a + T4b
- T4d — Inflammatory breast cancer
Board Pearl
Pectoralis muscle invasion does NOT qualify as T4 (chest wall). Chest wall = serratus anterior, intercostals, or ribs. Muscle enhancement on MRI alone does not change stage; patient still gets radical mastectomy with pec major and minor removal.
Board Pearl
Paget disease is not T4 by itself. If Paget is associated with DCIS only → Tis. If associated with invasive cancer → staged by tumor size. If Paget disease causes tumor ulceration of the nipple → T4.
Imaging and Tumor Measurement
- Tumor size based on pathology (invasive component of the largest mass)
- Only the longest dimension used for staging
- Multifocal/multicentric disease is NOT accounted for in T stage
- Imaging may help when the cancer is very small (mostly removed at core biopsy) or in setting of NAC
- US measurements including echogenic rim best correlate with histologic size
- MRI measurements correlate best with pathologic size (especially ILC)
Node Staging (N)
| Stage | Criteria |
|---|---|
| N0 | No regional LN metastasis |
| N1 | Metastasis to 1–3 axillary LNs and/or tiny metastasis in internal mammary LNs on SLNB |
| N2 | Metastasis to 4–9 axillary LNs OR internal mammary LN involvement without axillary |
| N3 | ≥ 10 axillary LNs OR infraclavicular (Level III) OR supraclavicular |
N3 details:
- N3a — Ipsilateral infraclavicular (Level III) LNs ± Level I/II
- N3b — Ipsilateral internal mammary LNs + Level I/II axillary
- N3c — Ipsilateral supraclavicular LNs ± Level I/II
Board Pearl
For staging: Levels I, II, and III + infraclavicular nodes are lumped together. N2 disease if ipsilateral internal mammary node involved in the absence of axillary mets (impacts radiation/treatment planning). Non-ipsilateral regional nodes (mediastinal, hilar, cervical, contralateral axillary) = M1 (distant) disease.
Skip Metastases
- Overall incidence: 2.6% (95% CI 1.8–3.6%) among all new invasive cancers
- In needle biopsy-proven metastatic cancers: 7.2% (Chung et al)
- Rotter nodes (interpectoral) often not taken on Level I/II dissection — important to evaluate on MRI
AJCC Staging Categories
| Category | Prefix | Based On |
|---|---|---|
| Clinical | c | Clinical exam, diagnostic imaging (mammo, US; MRI optional unless occult), and core biopsy |
| Pathologic | p | Surgical specimens including SLNB |
| Post-therapy | yp | After NAC, radiation, or hormonal therapy |
| Restaging | After recurrence |
Anatomic Stage Groups
| Stage | Definition |
|---|---|
| 0 | DCIS, no axillary or distant metastasis |
| I | Invasive tumor ≤ 2 cm, no distant metastasis |
| IA | No axillary LN metastasis |
| IB | Micrometastasis in 1–3 axillary LNs |
| IIA | Invasive tumor ≤ 2 cm with metastasis in 1–3 axillary LNs + tiny internal mammary LN mets on SLNB; OR invasive tumor > 2 cm but < 5 cm with no axillary or distant mets |
| IIB | Invasive tumor > 2 cm but < 5 cm with metastasis in 1–3 axillary LNs + tiny internal mammary LN mets on SLNB; OR invasive tumor > 5 cm without skin/chest wall, no axillary mets |
| IIIA | Tumor < 5 cm with axillary mets in 4–9 LNs or internal mammary LNs, no distant; OR tumor > 5 cm without chest wall/skin involvement with mets in up to 9 axillary LNs or enlarged internal mammary LNs |
| IIIB | Invasive tumor of any size grown into skin or chest wall, mets in 0–9 axillary LNs or internal mammary LNs, no distant. Includes inflammatory breast cancer. |
| IIIC | Invasive tumor of any size, mets in ≥ 10 axillary LNs OR Level III LNs OR supraclavicular LNs OR any axillary LNs with enlarged internal mammary LNs OR > 3 axillary LNs with micrometastasis in internal mammary LNs. No distant disease. |
| IV | Any size or nodal status with distant metastasis |
5-Year Survival Rates
| Stage | 5-Year Survival |
|---|---|
| 0 | 93% |
| IA | 88% |
| IB | 88% |
| IIA | 81% |
| IIB | 74% |
| IIIA | 67% |
| IIIB | 41% |
| IIIC | 49% |
| IV | 15% |
Lymph Node Evaluation
US Imaging of Axillary Nodes
- Metastatic deposits first seen in cortex, just under the capsule → cortical thickening (focal or diffuse)
- Focal cortical thickening > diffuse cortical thickening for malignancy
- Lymph fluid enters at cortex, drains out at hilum
Lymph Node Regions
- Regional (for staging): axillary Levels I/II/III, internal mammary, supraclavicular, infraclavicular
- Intramammary lymph nodes are classified as axillary nodes for staging purposes
- Distant (M1): mediastinal, hilar, cervical, contralateral axillary
Multifocal vs. Multicentric
| Term | Definition | Implication |
|---|---|---|
| Multifocal | Usually < 4 cm apart, along same ductal system | Multiple masses same quadrant |
| Multicentric | Usually 4–5 cm apart, different quadrant of ipsilateral breast | Usually contraindication to BCT |
Inflammatory Breast Cancer
- Not T4 because of size — any size with skin/chest wall involvement qualifies
- Diagnosis may be:
- Clinical: Red, swollen breast in patient with invasive carcinoma (NOT DCIS alone)
- Histologic: Punch biopsy showing invasion of dermal lymphatics
- Stage IIIB by definition
MRI in the Newly Diagnosed Patient
- Detects additional ipsilateral cancer not seen on mammo/US in 10–25% of women
- Detects contralateral cancer in 5.5% of women
- Meta-analysis (50 studies, >10,000 patients, 2012):
- 20% had ipsilateral disease (abnormal enhancement, not just cancer)
- 9.1% underwent more extensive surgery
- 4.6% were false positives (no cancer on excision)
- 10% underwent mastectomy due to MRI; 20% of those were false positives
- BCT local recurrence risk: 6% regardless of pre-op MRI
European Society of Breast Cancer Specialists Pre-Op MRI Indications
- ILC
- High-risk patients (genetic mutation or family history)
- < 60 yo with dense breasts (size discrepancy > 1 cm between mammo and US)
- Partial breast irradiation candidates (maybe also ER/PR negative, young age, dense tissue)
- Older/obese patients
- Men with breast cancer