Breast cancer classification

Breast cancer classification divides breast cancer into several categories according to multiple different schemes, each based on different criteria and serving a different purpose. A typical description usually considers each of these aspects in turn: the histolopathological type, the grade of the tumor, the stage of the tumor, and the expression of proteins and genes.

The American Joint Committee on Cancer (AJCC) staging system provides a strategy for grouping patients with respect to prognosis. Therapeutic decisions are formulated in part according to staging categories but primarily according to lymph node status, estrogen- and progesterone-receptor levels in the tumor tissue, menopausal status, and the general health of the patient. 

Classification of breast cancer is usually, but not always, primarily based on the histological appearance of tissue in the tumor. A variant from this approach, defined on the basis of physical exam findings, is that inflammatory breast cancer (IBC), a form of ductal carcinoma or malignant cancer in the ducts, is distinguished from other carcinomas by the inflamed appearance of the affected breast, which correlates with increased cancer aggressivity.

 The practical purpose of classification is to describe each individual instance of breast cancer in a way that helps select which treatment approach is anticipated to have the best chance for a good outcome, with increased efficacy and low toxicity. Treatment algorithms rely on breast cancer classification to define specific subgroups that are each treated according to the best evidence available. Classification aspects must be carefully tested and validated, such that confounding effects are minimized, making them either true prognostic factors, which estimate disease outcomes such as disease-free or overall survival in the absence of therapy, or true predictive factors, which estimate the liklihood of response or lack of response to a specific treatment.

Stage Information

The American Joint Committee on Cancer (AJCC) staging system provides a strategy for grouping patients with respect to prognosis. Therapeutic decisions are formulated in part according to staging categories but primarily according to lymph node status, estrogen- and progesterone-receptor levels in the tumor tissue, menopausal status, and the general health of the patient.

The AJCC has designated staging by TNM classification.

Primary tumor (T):

TX: Primary tumor cannot be assessed T0: No evidence of primary tumor Tis: Carcinoma in situ; intraductal carcinoma, lobular carcinoma in situ, or

Paget's disease of the nipple with no associated tumor. Note: Paget's disease associated with a tumor is classified according to the size of the tumor.

T1: Tumor 2.0 cm or less in greatest dimension

T1mic: Microinvasion 0.1 cm or less in greatest dimension T1a: Tumor more than 0.1 but not more than 0.5 cm in greatest dimension T1b: Tumor more than 0.5 cm but not more than 1.0 cm in greatest dimension T1c: Tumor more than 1.0 cm but not more than 2.0 cm in greatest dimension

T2: Tumor more than 2.0 cm but not more than 5.0 cm in greatest dimension T3: Tumor more than 5.0 cm in greatest dimension T4: Tumor of any size with direct extension to (a) chest wall or (b) skin,

only as described below. Note: Chest wall includes ribs, intercostal muscles, and serratus anterior muscle but not pectoral muscle.

T4a: Extension to chest wall T4b: Edema (including peau d'orange) or ulceration of the skin of the

breast or satellite skin nodules confined to the same breast

T4c: Both of the above (T4a and T4b)
T4d: Inflammatory carcinoma*

*Note: Inflammatory carcinoma is a clinicopathologic entity characterized

by diffuse brawny induration of the skin of the breast with an erysipeloid edge, usually without an underlying palpable mass.¹ Radiologically there may be a detectable mass and characteristic thickening of the skin over the breast. This clinical presentation is due to tumor embolization of dermal lymphatics with engorgement of superficial capillaries.

Regional lymph nodes (N):

NX: Regional lymph nodes cannot be assessed (e.g., previously removed) N0: No regional lymph node metastasis N1: Metastasis to movable ipsilateral axillary lymph node(s) N2: Metastasis to ipsilateral axillary lymph node(s) fixed to each other or

to other structures

N3: Metastasis to ipsilateral internal mammary lymph node(s)

Pathologic classification (pN):

pNX: Regional lymph nodes cannot be assessed (not removed for pathologic

study or previously removed)

pN0: No regional lymph node metastasis
pN1: Metastasis to movable ipsilateral axillary lymph node(s)

pN1a: Only micrometastasis (none larger than 0.2 cm) pN1b: Metastasis to lymph node(s), any larger than 0.2 cm

pN1bi: Metastasis in 1 to 3 lymph nodes, any more than 0.2 cm and all

less than 2.0 cm in greatest dimension

pN1bii: Metastasis to 4 or more lymph nodes, any more than 0.2 cm and

all less than 2.0 cm in greatest dimension

pN1biii: Extension of tumor beyond the capsule of a lymph node

metastasis less than 2.0 cm in greatest dimension

pN1biv: Metastasis to a lymph node 2.0 cm or more in greatest dimension

pN2: Metastasis to ipsilateral axillary lymph node(s) fixed to each other

or to other structures

pN3: Metastasis to ipsilateral internal mammary lymph node(s)

Distant metastasis (M):

MX: Presence of distant metastasis cannot be assessed M0: No distant metastasis M1: Distant metastasis present (includes metastasis to ipsilateral

supraclavicular lymph nodes)

AJCC stage groupings

Stage 0 ;

Tis, N0, M0

Stage I ;

T1,* N0, M0

*T1 includes T1mic

Stage IIA ;

T0, N1, M0 T1,* N1,** M0 T2, N0, M0 *T1 includes T1mic **The prognosis of patients with pN1a disease is similar to that of patients

with pN0 disease.

Stage IIB ;

T2, N1, M0 T3, N0, M0

Stage IIIA ;

T0, N2, M0 T1,* N2, M0 T2, N2, M0 T3, N1, M0 T3, N2, M0 *T1 includes T1mic

Stage IIIB ;

T4, Any N, M0 Any T, N3, M0

Stage IV ;

Any T, Any N, M1 Stage Information for Breast Cancer

References

1. Breast. In: Edge SB, Byrd DR, Compton CC, et al., eds.: AJCC Cancer Staging Manual. 7th ed. New York, NY: Springer, 2010, pp 347-76.
2. Singletary SE, Allred C, Ashley P, et al.: Revision of the American Joint Committee on Cancer staging system for breast cancer. J Clin Oncol 20 (17): 3628-36, 2002.  [PUBMED Abstract]
3. Woodward WA, Strom EA, Tucker SL, et al.: Changes in the 2003 American Joint Committee on Cancer staging for breast cancer dramatically affect stage-specific survival. J Clin Oncol 21 (17): 3244-8, 2003.  [PUBMED Abstract]