Effect of Radiotherapy after Breast-conserving Surgery in Elderly Patients with Early Breast Cancer according to the American Joint Committee on Cancer 8th Edition Breast Cancer Staging System in Japan

概要

Background: American Joint Committee on Cancer (AJCC) 8th Edition Breast Cancer Staging System added biological information in addition to traditional TNM staging, but its prognostic impact in Japanese patients treated with postoperative radiotherapy(RT) has not been discussed. The number of elderly patients in Japan with breast cancer has been gradually increasing. Whether RT can provide substantial benefit for elderly patients after breast-conserving surgery (BCS) is controversial. In this study, I retrospectively analyzed the data from my institution using the AJCC 8th edition staging manual.

Methods: Patients who were treated with postoperative radiotherapy for breast cancer in our institution between January 2011 and December 2015 were restaged by the AJCC 8th pathological prognosis staging system, and then overall survival (OS), disease-free survival (DFS) rates and hazard ratios (HR) were analyzed to compare the predictive fit of the two staging systems. Then I reviewed patients age ≥65 years who received BCS and adjuvant RT or BCS alone for breast cancer between 2010 and 2015 in our institution, and I restaged those patients using the AJCC 8th edition pathological prognostic staging system. I compared relapse-free survival(RFS) rates and OS rates in the RT group and no RT group.

Results: A total of 507 patients who in whom postoperative RT was performed for breast cancer were enrolled. 36.1% patients were downstaged and 5.3% patients were upstaged from the 7th to 8th editions staging system classification. Kaplan–Meier curves and HRs showed differences in OS and DFS rates between the 7th edition and 8th edition staging systems. Then 170 patients aged 65 years or older were eligible for analysis: 94 (55.3%) were treated with RT and 76 (44.7%) were treated without RT. Age (p<0.01) was associated with the use of RT. Adjuvant RT significantly improved RFS (95.75% vs 84.21%, p=0.02). There was no significant difference between the OS rates in the two groups. Univariate analysis showed that pathologic T stage and N stage were significantly associated with both RFS and OS and that histologic grade, chemotherapy, HER2, and RT were significantly associated with RFS but not with OS. RT reduced the risk of recurrence (HR: 0.56, 95% CI: 0.19-0.96, P=0.04).

Conclusions: Compared with the 7th edition in breast cancer, AJCC 8th edition prognostic stage system has more precise stratification and superior prognostic value, providing a more accurate reference for the choice of radiotherapy for patients with breast cancer in Japan. Adjuvant RT after BCS was associated with significantly improved RFS but had no significant impact on OS in elderly patients with early breast cancer according to the AJCC 8th edition staging system in Japan. With modern RT technology and capabilities, adjuvant RT should be performed even for elderly patients with breast cancer. RT strategy for breast cancer should be decided considering the prognostic factors and individual status rather than age alone.