ESTRO 2021 Abstract Book

S7

ESTRO 2021

through PROMs before the start of treatment for BC and afterwards to allow us to measure the concrete effect of treatments.

SP-0021 Less surgery or less radiation therapy in early stage breast cancer? P. Poortmans 1 1 Iridium Netwerk & Antwerp University, Radiation oncology, Wilrijk-Antwerp, Belgium

Abstract Text Breast cancer is the most common cancer in women in the industrialised western countries. Moreover, there is a worldwide increase in age-standardized incidence over the last decades. Simultaneously, mortality rates decreased clearly in the industrialised western countries, leading to a current ratio of 1 death for every 6 diagnosis per year compared to 1 death per 2.5 diagnoses 40 years ago. Current research to explore a decrease of the burden of radiation therapy for breast cancer entails precise tailoring of the extent, rather than completely omitting radiation therapy. Possible options include lowering the total dose, omission of the boost, hypofractionation and the selective introduction of partial breast irradiation. Importantly, modern radiation therapy techniques including anatomy-based target volume contouring lead to a decrease in the size of the irradiated volumes, facilitating the use of hypofractionation. Elective regional nodal irradiation has been demonstrated in several randomised trials and meta-analyses to significantly impact on locoregional control, disease-free survival, breast cancer mortality and overall survival. The generalizability of these results remains complex in the light of the decreasing use of axillary lymph node dissection, the use of more effective adjuvant systemic therapy, the increasing use of primary systemic therapy and, last but by far not least, continuously improving radiation therapy techniques. In general, radiation therapy tends to compensate for the decreasing extent of surgery to the breast and the axillary lymph nodes, eliminating postoperatively remaining residual tumour cells while maintaining better aesthetic and functional results. As a drawback in some occasions, however, the indications for the extent of radiation therapy have to be assessed on less extensive pathological staging information as we were used to in the past. Research is on-going to individualise radiation therapy also more on the basis of biological factors including gene expression profiles. When considering age, treatment decisions should rather be based on biological age instead of calendric age. The evolution of our understanding of breast cancer biology, evolution and treatment greatly stimulated the use of primary systemic treatment, also in early stages with minimal or absent lymph node involvement at diagnosis, especially in the case of unfavourable molecular subtypes. The role of both surgery and radiation therapy after a good tumour response, is currently questioned by various studies. SP-0022 Tumour bed boost in breast cancer - When, whom, how? M. Krause 1 1 University Hospital and Faculty of medicine C.G. Carus, Technische Universität Dresden, Radiation Oncology/ OncoRay, Dresden, Germany Abstract Text After the seminal boost-trial published in 2001 1 , showing an improvement of local tumour control, tumour bed boosts were introduced in clinical guidelines and were widely used in large cohorts of breast cancer patients. On the other hand, additional boost dose application can impact cosmetic outcome of radiotherapy and at the same time, considerable advances were made in systemic treatment of breast cancer, also impacting local tumour control rates. This led to more effort in selection of patients who potentially profit from boost application. Also, several boost techniques have been evaluated, including photon or electron techniques, but also intraoperative radiotherapy boosts. The advent of hypofractionated radiotherapy has led to approaches of simultaneous integrated boost concepts. The talk will give an overview on current evidence for boost dose application in breast cancer as well as an the most important open questions in this area. 1. Bartelink, H. , et al. Recurrence rates after treatment of breast cancer with standard radiotherapy with or without additional radiation. N Engl J Med 345 , 1378-1387 (2001). SP-0023 Less endocrine therapy for very low-risk patients? E. Nowicka 1 1 Maria Skłodowska-Curie National Research Institute of Oncology, III Department of Radiotherapy and Chemotherapy, Gliwice, Poland Abstract Text In low risk breast cancer patient treatment, the question arises about optimal adjuvant treatment, after conserving surgery. According to guidelines, is based on radiotherapy alone or in combination with hormonal therapy in receptor positive tumor. It is well known that radiotherapy (RT) offers a benefit in term of local control, however the absolute risk reduction with the addition of radiotherapy in this population is low, with no OS gain. All receptor positive patients are offered additional 5 years of endocrine therapy (ET). Tamoxifen and aromatase inhibitors (AI) are options, but AIs have increased benefit. Excellent prognosis with low risk of local recurrences should be weighed against treatment complications and treatment burden. The vast majority of death in older low risk breast cancer patients are from other causes not breast cancer. Age and related comorbidities are the main risk factors of death with respect to breast cancer and for this reason, the choice of the adjuvant treatment in older age is still debated. These factors not only influence clinician’s decision to prescribe endocrine therapy or the type of radiotherapy. What’s also important the patients’ ability to comply with long term therapy is influenced by their health condition too. The endocrine therapy (ET) prescription slightly decrease in older patients and in those with severe comorbidity index, and is connected with additional risk of complications. Adverse effects are not common, but can lead to poor adherence and non-persitence and worsen the quality of life. Several clinical trials addressed the issue of