AJCC 9th Edition TNM Staging: What Changed for Breast Cancer

What's new in the 9th edition

The AJCC Cancer Staging Manual, 9th edition continues the shift toward integrating tumor biology with anatomy. For breast cancer, estrogen receptor (ER), progesterone receptor (PR), HER2, and grade remain central to the prognostic stage groups, while histologic grade and multifocality continue to inform staging decisions.

Implications for breast cancer staging

Accurate T, N, and M assignment still depends on careful imaging and pathology. The prognostic stage group combines anatomic extent with biomarker status, so two patients with the same TNM can land in different stage groups based on receptor biology.

Putting it into practice

• Confirm ER/PR/HER2 status before finalizing the prognostic group.
• Use the anatomic stage and prognostic stage together when discussing prognosis.
• Re-stage after neoadjuvant therapy using the post-treatment (yp) classification.

A structured staging tool helps keep these inputs consistent across cases.