ESTRO 2020 Abstract book

S366 ESTRO 2020

survivorship issue.

PH-0597 Radiation and/or endocrine therapy? Recurrence outcomes in low-risk breast cancer patients over 70 H. Dahn 1 , D. Wilke 1 , G. Walsh 2 , J. Pignol 1 1 Dalhousie University, Department of Radiation Oncology, Halifax, Canada ; 2 Dalhousie University, Department of Epidemiology, Halifax, Canada Purpose or Objective Women over 70 with early breast cancer treated with breast-conserving surgery are typically offered adjuvant endocrine therapy and radiation therapy. Prior studies have supported the omission of adjuvant radiation in this low-risk population. We sought to compare the effect of adjuvant treatment with endocrine therapy alone, radiation therapy alone or both versus no adjuvant treatment on local control and survival in a population of low-risk breast cancer patients over 70 years of age. Material and Methods Following local research ethics board approval, data was extracted on 1,363 low-risk breast cancer patients over the age of 70 treated with a breast-conserving surgery in Nova Scotia from 2003 until 2018. 460 patients met inclusion criteria of T1N0 invasive disease with negative margins and not treated with chemotherapy. The primary outcome was local recurrence-free survival at 5 and 10 years. Secondary outcomes included loco-regional recurrence-free survival, distant metastasis-free survival, disease-free survival and overall survival. Results Patients receiving no adjuvant therapy had worse local recurrence-free, loco-regional recurrence-free and disease-free survival than patients receiving at least one form of adjuvant therapy (p < 0.05). 5 year local- recurrence rates were 0.8% in patients receiving both endocrine and radiation therapy, 1.5% in those receiving radiation alone, 4.2% in those receiving endocrine therapy alone and 12% in those receiving no adjuvant therapy. There was no statistically significant difference for patients receiving at least one adjuvant therapy. On multivariate cox proportional hazard analysis, adjuvant endocrine therapy and adjuvant radiation therapy were statistically associated with local recurrence-free survival, while the tumor size, grade, LVI status and margin status were not. No significant difference in distant metastasis- free survival was seen between treatment groups.

PH-0596 Whole breast irradiation in comparison to endocrine therapy in early stage breast cancer J. Haussmann 1 , W. Budach 1 , S. Corradini 2 , B. Tamaskovics 1 , E. Boelke 1 , F. Djiepmo-Njanang 1 , K. Kammers 3 , C. Matuschek 1 1 University Hospital Düsseldorf, Radiation Oncology, Düsseldorf, Germany ; 2 Ludwig-Maximilians-University, Radiation Oncology, Munich, Germany ; 3 The Johns Hopkins University School of Medicine, Division of Biostatistics & Bioinformatics- Department of Oncology, Baltimore, USA Purpose or Objective Multiple randomized trials have established adjuvant endocrine therapy (ET) and whole breast irradiation (WBI) as the standard approach after breast conserving surgery (BCS) in early stage breast cancer. The omission of WBI has likewise been studied in multiple trials and resulted in reduced local control with maintained survival rates and has therefore been adapted as a treatment option in selected patients in several guidelines. Omitting ET instead of WBI might also be a valuable option as both treatments have distinctly different side effect profiles. However the clinical outcomes of BCS+ET vs. BCS+WBI have not been thoroughly analyzed. Material and Methods We performed a systematic literature review searching for randomized trials comparing BCS+ET vs. BCS+WBI in low risk breast cancer patients with publication dates after 2000. We excluded trials using any form of chemotherapy, regional nodal radiation and mastectomy. The meta- analysis was performed using a two step process. First, the published individual patient EBCTCG data (IPD) were used to allow a direct and indirect comparison for overall survival (OS) and breast cancer-specific survival (BCSS). Second, we extracted all available published event rates and the effect-sizes for OS, BCSS, local- (LR) and regional recurrences (RR), recurrence-free interval (RFI), disease- free survival (DFS), distant metastases-free interval (DMFI), contralateral breast cancer (CBC), second cancer other than breast cancer (SCNBC) and mastectomy-free interval (MFI) as investigated endpoints and compared them in a network meta-analysis. Statistical analysis was performed using the Microsoft Excel add-in MetaXL 5.3 utilizing the inverse variance heterogeneity model. Results We identified three studies including a direct a comparison of BCS+ET vs. BCS+WBI (n=1059) and nine studies randomizing overall 5786 patients additionally to BCS only and BCS+WBI+ET resulting in 4 arms. Using IPD OS and BCSS were not significantly different between BCS+ET and BCS+WBI after 10 years (OR=0.85; CI95%:0.59-1.22; p=0.369) and (OR=0.72; CI95%:0.38-1.36; p=0.305). In the network-analysis LR was significantly lower in the BCS+WBI group in comparison to the BCS+ET group (HR=0.62; CI95%:0.42-0.92; p=0.019).RR, RFI and DFS were not different between the two approaches. We also did not find any differences in OS (HR=1.00; CI95%:0.63-1.59; p=0.984) and BCSS (OR=1.18; CI95%:0.28-4.97; p=0.823). Further, we found a lower DMFI, a higher rate of CBC and a reduced MFI in the BCS+WBI-arm. Conclusion Evidence from direct and indirect comparison suggests that BCS+WBI without ET might be an equivalent de- escalation strategy to BCS+ET in low risk breast cancer. Adverse event rates and quality of life measures have to be further compared between these approaches.