Abstract PO3-15-08: Validation for prognostic staging based AJCC 8th edition with nuclear grade in Japanese breast cancer patients: A multicenter retrospective study
Authors: Kaneshiro Kazuhisa , Yamada Mai , Hayashi Saori , Koga Kenichiro , Saimura Michiyo , Otomo Naoki , Umeda Shuyo , Anan Keisei , Okido Masayuki , Morisaki Takafumi , Nakamura Masafumi , Kubo Makoto 
Published: May 2024

Abstract
Introduction.
The American Joint Committee on Cancer (AJCC) 8th edition of breast cancer classification introduced the concept of "prognostic stage," which is based on anatomic classification (TNM classification) plus four biomarkers: estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor (HER2), and histological grading (HG).
In Japan, however, the introduction of histological classification has been passive and slow, and the nuclear grading (NG) has been used so far.
Objective.
Our aim is to compare the prognostic staging classification in the AJCC, 8th edition which substitutes NG for HG (AJCC8th-NG) with the TNM classification, and to confirm the usefulness of AJCC8th-NG classification.
Methods.
We collected 5229 patients with primary breast cancer operated on between 2005 and 2013 at six institutions affiliated with Kyushu University Hospital in Japan, for whom prognosis was available.
We retrospectively evaluated the 7-year survival rates based on the TNM classification and the AJCC8th-NG classification, based on the pathological diagnosis of their surgeries.
Results.
Median age was 58 years (24-99), 5210 (99.6%) were female, and the 7-year survival rate of all eligible patients was 93.2%.
The changes in the number of cases by stage were observed as follows: Stage 0 (16.5%), Stage IA (42.3% to 56.2%), Stage IB (0.3% to 8.8%), Stage IIA (21.5% to 6.9%), Stage IIB (9.7% to 3.1%), Stage IIIA (3.9% to 3.5%), Stage IIIB (1.5% to 1.9%), Stage IIIC (2.1% to 0.9%), Stage IV (1.9%).
The changes in 7-year survival rates were observed as follows: Stage 0 (96.1%), Stage IA (96.8% → 96.5%), Stage IB (93.7% → 93.4%), Stage IIA (93.1% → 87.8%), Stage IIB (88.5% → 84.6%), Stage IIIA (86.9% → 80.4%), Stage IIIB (78 .7% to 84.4%), Stage IIIC (79.8% to 58.4%), and Stage IV (51.9%). (TNM classification →AJCC8th-NG classification)
Both TNM classification and AJCC8th-NG classification were significantly associated with prognosis. AJCC8th-NG classification was more stratified. In AJCC 8th-NG Stage IB, which is the largest population in all patients, 42% of that were triple-negative type (TN) downstaging from TNM Stage IA and 58% were luminal type downstaging from TNM Stage II-IIIA. In AJCC 8th-NG Stage IIIC, which was changed the most with biomarkers, 52% of that were TN upstaging from TNM Stage IIIA-IIIB. On the other hand, 50% of AJCC 8th-NG Stage IIIB with a favorable prognosis were ER-positive or HER2-positive downstaged from TNM Stage IIIC.
Discussion
TN breast cancer generally has a poor prognosis. However, HER2-positive breast cancer, which used to have a poor prognosis, is said to have a favorable prognosis after the availability of anti-HER2 drugs. This time, we examined cases after 2005 when anti-HER2 drugs became available in Japan, but the results did not show that HER2-positive breast cancer had a better prognosis than HER2-negative breast cancer. In this study, we were unable to confirm the use of anti-HER2 drugs. In the AJCC 8th classification, it seems necessary to consider whether or not treatment is being provided. If all patients are treated, the prognostic stratification will become clearer.
Conclusion.
Our study could show that AJCC8th-NG classification was useful for predicting prognosis same as AJCC8th classification in the relatively large cohort.
Citation Format: Kazuhisa Kaneshiro, Mai Yamada, Saori Hayashi, Kenichiro Koga, Michiyo Saimura, Naoki Otomo, Shuyo Umeda, Keisei Anan, Masayuki Okido, Takafumi Morisaki, Masafumi Nakamura, Makoto Kubo. Validation for prognostic staging based AJCC 8th edition with nuclear grade in Japanese breast cancer patients: A multicenter retrospective study [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-15-08.