Abstract PS1-01: Combined analysis of the WORTH 1 and WORTH 2 studies of ipsilateral breast tumor recurrence after breast conservative surgery without radiotherapyusing the “5-mm thick slice and 5-mm free margin method”

Abstract

Abstract Background: Breast conserving surgery with radiotherapy is one of the standard treatment methods for early breast cancer. However, it is regarded as an option to treat elderly patients with small hormone receptor positive breast cancer with breast conserving surgery and hormone therapy without radiotherapy. Two sequential prospective studies were conducted to examine the efficacy of breast conserving surgery without radiotherapy from 2002. Patients and Methods: Primary breast cancer patients were divided into the WORTH 1 (n=123) group (Oct. 2002 and Mar. 2005) and the WORTH 2 (n=198) group (Dec. 2006 and Nov. 2011) and the data was retrospectively combined and analyzed. The eligibility criteria of the two sequential studies were a tumor ≥3cm determined by palpation, pathologically node negative by axillary dissection or sentinel node biopsy and M0, no preoperative treatment, postmenopausal patients ≥50 years of age at surgery, no tumor cells within 5 mm from the margins, no lymphatic invasion around the primary tumor, and estrogen receptor positive. The surgical specimens were sliced at 5 mm intervals and all the slices were examined microscopically. Postoperative radiotherapy was not conducted and adjuvant chemotherapy was optional. The patients were treated with tamoxifen or anastrozole in WORTH 1 and anastrozole in WORTH 2 for 5 years. Ipsilateral breast tumor recurrence (IBTR)-free survival and distant relapse-free survival (DRFS) were recorded as the interval from initial surgery until IRTR or distant relapse. The factors related to IBTR were evaluated using the proportional hazard model. Patients who did not develop IBTR or distant relapse were statistically censored at the time of the last follow-up or death. Survival rates were calculated using the Kaplan-Mayer method. Statistical analyses were conducted using the log rank test. Values < 0.05 were considered statistically significant. Results: The median age at surgery was 65 (range 50-84). The median tumor size was 1.5 cm (range 0-4.0 cm). The median follow-up period for IBTR was 95 months (range 4-192 months). Only 3 patients were treated with adjuvant chemotherapy. The 5- and 10-year overall survival rates were 98.7% and 95.1%, respectively and the 5- and 10-year distant DRFS rates were 99.3% and 96.3%, respectively. The 5- and 10-year IBTR free rates were 97.0% and 89.7%, respectively. Older patients had significantly less IBTR rates (5-year IBTR free rates: 95.8% for ≤64 vs. 98.1% for ≥65, p=0.019). There was no difference in IBTR rates between the large and small tumors (5-year IBTR free rates: 96.9% ≤1.4 cm vs. 96.8% for ≥1.5 cm, p=0.094). PR positivity had a significantly lower IBTR free rates (5-year IBTR free rates: 98.3% for PR positive vs. 91.5% for PR negative, p=0.009). The age at surgery (≤64, p=0.017, Hazard ratio 3.07, 95% CI 1.22-7.70) and the PR status (PR negative, p=0.024, Hazard ratio 2.54, 95% Cl 1.13-5.69) independently affected the IBTR rates. Both the 5- and 10-year IBTR free rates of the patients who were ≥65 at surgery and had PR positive tumors (n=136) were 98.4%. Conclusions: The findings suggest that the “5-mm thick slice and 5-mm free margin” method may be effective in selecting patients who can be treated with breast conserving surgery and hormone therapy without radiotherapy. Citation Format: Norikazu Masuda, Shozo Ohsumi, Reiki Nishimura, Sadako Akashi-Tanaka, Kimito Suemasu, Hideko Yamauchi, Eriko Tokunaga, Tadashi Ikeda, Tsunehiro Nishi, Hiroto Hayashi, Yuichi Iino, Yuichi Takatsuka, Hideo Inaji. Combined analysis of the WORTH 1 and WORTH 2 studies of ipsilateral breast tumor recurrence after breast conservative surgery without radiotherapyusing the “5-mm thick slice and 5-mm free margin method” [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS1-01.