Breast Cancer Staging

Dr Shiroma De Silva-Minor, distinguished consultant breast oncologist, explains breast cancer staging, detailing the classification system and its impact on treatment.

Breast cancer staging is a system we use to describe the extent of cancer in the body. It helps us determine how far the cancer has spread, which informs both prognosis and treatment planning.

We use the TNM system to stage breast cancer, which stands for Tumour (T), Node (N), and Metastasis (M).

T - Tumour Size

T0: No evidence of the primary tumour (this is rare in breast cancer).
Tis- Carcinoma in situ, meaning the cancer cells are still confined to the ducts or lobules where they began and have not invaded surrounding breast tissue.
T1: The tumour is small, 2 cm or less in size.
T2: The tumour is between 2 and 5 cm.
T3: The tumour is larger than 5 cm in size.
T4: The tumour has invaded into the chest wall or skin, indicating more advanced local spread.

N - Lymph Node Involvement

N0: No lymph nodes are involved.
N1: Cancer has spread to 1-3 nearby lymph nodes (usually under the arm).
N2: Cancer is found in 4-9 lymph nodes.
N3: Cancer has spread to 10 or more lymph nodes or involves lymph nodes in the internal mammary chain (behind the breastbone).

M - Metastasis

M0: No evidence of distant metastasis, meaning the cancer hasn't spread to other parts of the body beyond the breast and regional lymph nodes.
M1: The cancer has spread to distant organs, such as the lungs, liver, bones or brain. This is considered stage IV or metastatic breast cancer.

Stages

Using the TNM information, we categorise breast cancer into stages from 0 to IV:

Stage 0: Non-invasive cancer or carcinoma in situ (DCIS/LCIS).
Stage I: Early-stage invasive cancer, with a small tumour and no or minimal lymph node involvement (T1, N0-N1, M0).
Stage II: Larger tumours (T2 or T3) or more extensive lymph node involvement (N1-N2), but still no distant metastasis.
Stage III: Locally advanced cancer, with larger tumours and/or significant lymph node involvement (T3 or T4, N2-N3), but still no distant metastasis.
Stage IV: Any cancer with distant metastasis (M1), regardless of the size of the tumour or lymph node involvement.

This internationally-agreed staging convention means that patients with similar stages can be enrolled into clinical trials, from different centres or even different countries. This then allows a comparison of the treatment outcomes based on stage.

Early-stage cancer is usually Stage I or II. Treatments usually involve a combination of surgery, systemic anti-cancer therapy or radiotherapy, depending on the tumour biology. Locally advanced cancers (Stage III) may require a combination of chemotherapy, surgery and radiation. Stage IV breast cancer typically involves systemic therapies like chemotherapy, hormone therapy, targeted therapy or immunotherapy to control the disease.

Understanding the cancer stage provides a framework to offer the most effective treatment plan tailored to your specific situation.