ESTRO 2021 Abstract Book

S258

ESTRO 2021

D. Gabrys 1 , R. Kulik 2 , D. Graupner 3 , T. Latusek 1 , I. Debosz-Suwinska 1 , A. Roch-Zniszczol 1 , A. Namysl-Kaletka 1 1 Maria Sklodowska - Curie National Research Institute of Oncology, Gliwice Branch, Radiotherapy Department, Gliwice, Poland; 2 Maria Sklodowska - Curie National Research Institute of Oncology, Gliwice Branch, Radiotherapy Planning Department, Gliwice, Poland; 3 Maria Sklodowska - Curie National Research Institute of Oncology, Gliwice Branch, III Department of Radiotherapy and Chemotherapy, Gliwice, Poland Abstract Text Metastatic breast cancer is mostly an incurable disease, but in clinical practice, we can find long-term survivors. Some patients achieve a complete response (CR) and remain free of disease even beyond 20 years. They are usually young, with good performance status and oligometastatic disease. The line between oligometastatic disease and polymetastatcic is very thin. The definition of oligometastases varies in the literature, but the exact number of metastatic lesions usually does not exceed 5 and involved organs usually do not exceed 2. The treatment of metastatic breast cancer mostly relies on systemic therapy and for many years, radiation has been used for palliative purposes only . However, in recent decades, there has been growing interest in the use of metastasis-directed treatment mostly in patients presenting with limited metastatic disease, with a more favorable breast cancer molecular subtype and indolent disease . Therefore, in some patients, we can delay systemic therapy, or even in some cases it can be avoided. This is possible because t remendous technological progress has been made in the field of radiation oncology. Advances in both software and hardware allow to integrate body imaging with accurate treatment delivery methods. One such innovation has been the development of efficient stereotactic body radiotherapy (SBRT), which is defined as the non-invasive, precise and accurate delivery of highly conformal, image-guided and hypofractionated EBRT. In SBRT fewer fractions are used, shorter and faster treatment is more convenient for patients, moreover higher doses are potentially more effective. The management of metastatic breast cancer disease requires not only multidisciplinary tumour board decisions with individualized oncologic treatment options but also the consideration of patients' needs, expectations and priorities. Actually , patients are increasingly actively involved in making decision process about their treatment, taking into account the potential side effects that are related to it. There is a greater emphasis not only on the effects of oncological treatment but also on the quality of life after it is finished. In this context, radiotherapy may be important in the management of patients with metastatic breast cancer ameliorate clinical outcomes with limited toxicity. This presentation will review the rationale for SBRT, provide potential clinical settings that radiotherapy may be successfully incorporated in the management of metastatic breast cancer. The use of SBRT is gaining attention due to its safety profile, non-invasive nature, and defined effectiveness in cost-effective achievement of extended local control. Evidence for SBRT use in metastatic breast cancer patients is mostly limited to retrospective trials with a small number of patients. Therefore, prospective randomized controlled trials and research in genomic and molecular profiling are needed to characterize metastatic breast cancer patients who will most likely benefit from such a treatment and to draw a reliable conclusion. The current clinical and trial status of the treatment of metastatic breast cancer will be summarized. SP-0356 Concomitant radio-chemotherapy in a metastatic setting - Is it safe? C. Becherini 1 1 University of Florence - AOU Careggi, Radiation Oncology Unit, Oncology Department, , Firenze, Italy Abstract Text Radiation therapy (RT) and systemic agents’ combination could have pros and cons. Depending on their mechanism of action, anticancer drugs exert their impact preferentially in the G1 and S phases (most radioresistant) and sometimes in the G2 or M phase (most radiosensitive). The new anti-HER2 agents, cyclin-dependent kinases 4 and 6 (CDK4/6) inhibitors, and immunotherapy, all have the potential to be either radiosensitizing or radioinhibiting agents, yet there are few studies examining whether it is safe and effective for RT to accompany them for palliation or definitive treatment. Currently, we have limited data on anti-HER2 agents plus RT. To date, reliable conclusions about the toxicity of concomitant RT with anti-HER2 therapies are difficult to draw due to the heterogeneity of data. We should use caution when treating abdominal lesions with the two anti-HER2 agents plus RT due to increased gastrointestinal toxicity. Moreover, several case series reported that patients developed more radiation brain necrosis when T-DM1 and radiosurgery were given concurrently vs sequential . In summary, trastuzumab and RT can be given concurrently. Conversely, data are more limited on the newer anti-HER2 agents, pertuzumab and T-DM1. The concurrent use of CDK4/6 inhibitors and RT raises safety concerns as preclinical data enlightened their possible synergistic effect. Both are associated with neutropenia and fatigue, suggesting greater toxicity when concomitant. Currently prospective clinical data about CDK4/6 inhibitors and RT are scarce. Indeed, without confirmed safety proof, it seems wiser to suspend CDK4/6i five half-lives before and after RT. Not much is known about concurrent immunotherapy and RT, although it is possible the two could work together. In KEYNOTE-522 trial, initially, pembrolizumab was given in neoadjuvant setting and then restarted at least 2 weeks after RT. The protocol was amended to allow concurrent administration, as evidence emerged showing a synergistic effect without increased toxicity. There is a significant unmet need to define the therapeutic index of combining two treatment modalities that have experienced significant recent advances. While awaiting the results of the available ongoing prospective trials, caution should be paid, including careful patient selection, to avoid toxicity and compromise quality of life.

Proffered papers: Proffered papers 21: Motion management