Breast Cancer Stages and Classification

This is the seventh page in the Understanding Breast Cancer Guide. This guide was developed by the HealthTree Education Team and was last updated and reviewed on May 18, 2026.

Doctors use "stages" to describe how far cancer has grown and whether it has spread. Knowing the stage of your cancer helps your care team plan the best treatment and understand your prognosis.

For breast cancer, the stage is determined based on:

• The size of the tumor (T)
• Whether the cancer has spread to nearby lymph nodes (N)
• Whether the cancer has spread to distant organs, called metastasis (M)
• The biological features of the cancer, including hormone receptor status, HER2 status, and tumor grade

Knowing the stage of your cancer will help your care team plan your treatment and understand your prognosis.

The TNM Staging System

Most breast cancers are staged using the TNM system developed by the American Joint Committee on Cancer (AJCC). Your pathology report after surgery will include a detailed TNM designation. Each letter is assigned a number that describes how far the cancer has progressed in that category:

• T (Tumor) describes the size of the tumor and whether it has grown into nearby tissue, scored T1 to T4.
• N (Nodes) describes whether cancer has reached nearby lymph nodes, scoring N0 (none) to N3 (many lymph nodes or distant nodes).
• M (Metastasis) describes whether the cancer has spread to distant organs, scored M0 (no spread) or M1 (spread detected).

For breast cancer, the AJCC also incorporates biological factors (ER/PR status, HER2 status, and tumor grade) into the final stage assignment, which is why two patients with the same tumor size may have different stages.

Breast cancer stage groups

Often, TNM staging can be simplified into stages (0 through IV). The larger the number, the more advanced the cancer. 

Stage 0 — Non-Invasive Breast Cancer

Abnormal cells are found only within the milk duct (DCIS) or lobule (LCIS) and have not grown into surrounding breast tissue.

TNM example: Tis, N0, M0. The cancer is entirely contained within the duct or lobule and has not invaded nearby tissue, lymph nodes (N0), or distant organs (M0).

Stage I

The cancer is small and either has not spread to lymph nodes (Stage IA) or has spread to only a tiny cluster of cells in a nearby lymph node (Stage IB).

TNM example: T1, N0 or N1mi, M0. The tumor is 2 cm or smaller. Lymph nodes are either clear or have only tiny deposits of cancer cells. No distant spread (M0).

Stage II

The cancer has grown larger and/or has spread to a small number of nearby lymph nodes. Stage II is divided into IIA and IIB based on tumor size and lymph node involvement.

TNM examples:

• Stage IIA: T0 toT2, N1, M0 or T2, N0, M0. A small-to-medium tumor that has spread to 1 to 3 axillary lymph nodes, or a tumor up to 5 cm that has not spread to lymph nodes. No distant spread (M0).
• Stage IIB: T2, N1, M0 or T3, N0, M0. A medium tumor with limited lymph node spread, or a larger tumor (>5 cm) without lymph node involvement. No distant spread (M0).

Stage III

The cancer is larger and/or has spread to more lymph nodes or nearby tissue, but not to distant organs. Stage III is divided into IIIA, IIIB, and IIIC based on tumor size and lymph node spread.

TNM examples:

• Stage IIIA: T0 to T3, N2, M0 or T3, N1, M0. Cancer has spread to 4 to 9 axillary lymph nodes or to internal mammary lymph nodes. No distant spread (M0).
• Stage IIIB: T4, N0 to N2, M0. The tumor has grown into the chest wall or breast skin, causing swelling or ulceration (including inflammatory breast cancer). No distant spread (M0).
• Stage IIIC: Any T, N3, M0. Cancer has spread to 10 or more axillary lymph nodes, or to lymph nodes near the collarbone or internal mammary nodes. No distant spread (M0).

Stage IV (metastatic breast cancer)

The cancer has spread to distant organs. The most common sites of metastasis for breast cancer are the bones, liver, lungs, and brain.

TNM example:

• TNM example: Any T, Any N, M1. Cancer has spread to at least one distant organ (M1).

Recurrent breast cancer

Recurrent breast cancer is cancer that has come back after treatment. It may return in the same breast or chest area (local recurrence), in the lymph nodes (regional recurrence), or in distant organs (distant recurrence). Recurrent breast cancer is treated based on its stage and biological characteristics.