Validation of the new AJCC eighth edition of the TNM classification for breast cancer with a single-center breast cancer cohort.

Purpose: The new eighth edition TNM classification by the AJCC for breast cancer (BC) incorporates biologic factors and gene expression prognostic panels, in addition to traditional anatomic factors. In this study, we evaluated the prognostic value of this new staging system compared to the previous AJCC 7th edition staging system.

Methods: We conducted a retrospective analysis of women with stage I, II, or III BC who underwent curative surgery with/without adjuvant systemic therapy at Samsung Medical Center between July 2004 and December 2008.

Results: Of 3,208 BCs, this study was analyzed using the information of 2,790 BC patients. Hormone receptor-positive (HR+) and human epidermal growth factor 2 (HER2)- BCs were observed in 62.9% of BCs, HR+/ HER2+ in 9.3%, HR-/HER2- in 17.0%, and HR-/HER2+ in 10.8%. In survival analysis, we observed 245 distant recurrences and 198 deaths caused by BC progression. The median follow-up duration was 116.2 months. 10-year disease-specific survival (DSS) rates according to the AJCC 7th edition criteria were 97.2% of stage IA, 100% of IB, 94.9% of IIA, 87.9% of IIB, 86.4% of IIIA, 95.7% of IIIB, and 65.7% of IIIC (p < 0.001). After applying 8th edition criteria, the 10-year DSS rates were 98.1% of stage IA, 97.7% of IB, 93.8% of IIA, 92.7% of IIB, 88.2% of IIIA, 80.8% of IIIB, and 70.3% of IIIC (p < 0.001).

Conclusions: The AJCC 8th edition clinical staging system provides a good prognostic value and addresses the weakness of the AJCC 7th edition, which uses only anatomical pathologic staging.