Unofficial report by BreastGlobal team: Highlights and insights from the 18th St. Gallen Breast Cancer Conference 2023

INTRODUCTION The 18th St. Gallen International Breast Cancer Conference was held from 15th to 18th March 2023 in Vienna, Austria. This biennial event brought together leading breast oncologists, researchers and practitioners from around the world to discuss advancements and challenges in breast cancer treatment and research. In this report, we will discuss the key takeaways from the conference as presented by the team from BreastGlobal, Centre for Translational Cancer Research and Prashanti Cancer Care Mission, Pune, India. SUMMARY OF CONFERENCE SESSIONS Day 1, March 15, 2023, Vienna, Austria On the 1st day of the 18th St. Gallen International Breast Cancer Conference, the event commenced with a grand opening ceremony. This was followed by the highly anticipated award lectures for the St. Gallen Breast Cancer Award and the European School of Oncology (ESO) Umberto Veronessi Memorial Award. Giuseppe Viale from Italy delivered the St. Gallen Breast Cancer Award lecture, whereas Benjamin Anderson from Switzerland delivered the ESO Umberto Veronessi Memorial Award lecture. The day continued with a comprehensive overview of notable developments in breast cancer management since the previous edition of the conference in 2021. The spotlight was placed on various areas, including progress in local control through surgical and radiation measures, advancements in systemic therapy, translational research priorities, and the importance of survivorship and quality of life outcomes. Prominent presentations on the 1st day included discussions on surgery for patients with early breast cancer, access to evidence-based radiation therapy, novel systemic treatment approaches, translational research priorities and hot topics in survivorship and patient-reported outcomes.[1-3] A significant interactive session of the day revolved around a global discussion on the avoidance of unnecessary mastectomies and reconstructions. The session, chaired by Monica Morrow from the USA and Walter Weber from Switzerland, featured panellists from various countries, including Portugal, USA, Japan, Sweden, Slovenia, Saudi Arabia, Korea, China, Peru and Egypt. The discussion emphasised the superiority of conservative surgeries whenever feasible from an oncological perspective.[4-6] The session concluded with active audience participation, sharing opinions and a refresher on technical points for surgical oncologists. The day concluded with ample opportunities for socialising and collaborative networking during an Apero, allowing participants to engage in further discussions and build connections. Overall, the 1st day of the conference provided valuable insights into the latest advancements and emphasised the importance of evidence-based approaches and conservative surgical techniques in breast cancer management. Day 2, March 16, 2023, Vienna, Austria On day 2, the focus was primarily on systemic therapy options. The day commenced with a session on genomics, transcriptomics and circulating tumour DNA (ctDNA) for disease monitoring and risk stratification, chaired by Fabrice André (France) and Meredith Regan (USA). The topics covered during this session included the dynamics of ctDNA for early assessment of recurrence risk presented by Nicholas Turner (UK), the role of molecular imaging in breast cancer discussed by Michel van Kruchten (The Netherlands), the use of multiomic machine learning for predicting treatment response presented by Carlos Caldas (UK) and the assessment of clinical utility and validity of biomarkers in clinical trials presented by Meredith Regan (USA).[7-9] A panel discussion followed these presentations. The next session focussed on immunology in early breast cancer and was chaired by Sherene Loi (Australia) and Aleix Prat (Spain). The session explored various aspects, including the understanding of the anticancer immune response, innate and adaptive responses to breast cancer cells presented by Sherene Loi (Australia), the tumour microenvironment in early breast cancer discussed by Carsten Denkert (Germany), the use of multiplexed analysis and spatial histology to predict response presented by Marleen Kok (The Netherlands) and the future of breast cancer immunotherapy, particularly related to programmed death (PD) and programmed death ligand (PDL) vaccines, presented by Giuseppe Curigliano (Italy).[10-12] The subsequent session focussed on hereditary cancers and was chaired by Lisa Carey (USA) and Suzette Delaloge (France). The session covered topics such as imaging, screening and surveillance for individuals with increased hereditary breast cancer risk presented by Suzette Delaloge (France), local treatment in patients with high-risk hereditary breast cancer discussed by Maria Joao Cardoso (Portugal), management of patients harbouring medium penetrance genes presented by Christian Singer (Austria) and adjuvant systemic therapy for patients with germline BReast CAncer gene 1/2 (BRCA1/2) mutations presented by Andrew Tutt (UK).[13-15] A dedicated plenary session on future prospects in adjuvant settings followed, covering topics such as postneoadjuvant options in triple-negative disease, including poly adenosine diphosphate-ribose polymerase (PARP) inhibitors, capecitabine and checkpoint inhibitors presented by Javier Cortes (Spain), risk assessment in ER-positive disease and the use of cyclin-dependant kinases (CDKs) 4–6 inhibitors discussed by Angela De Michele (USA), antibody-drug conjugates for breast cancer therapy presented by Cristina Saura (Spain), and the integration of new oral oral selective estrogen receptor degraders (SERDs) in adjuvant treatment presented by David Cameron (UK).[15-17] The day concluded with two interactive sessions. The first was an intriguing debate titled ‘Early breast cancer: do we need chemotherapy in low genomic/high clinical risk (estrogen receptor (ER)+/human epidermal growth factor receptor (HER2)-)’ between Nadia Harbeck (Germany) and Lisa Carey (USA), chaired by Giuseppe Curigliano (Italy) and Micheal Gnant (Austria). The second session focussed on the choice of adjuvant treatment in cases where the stage and biology do not align, titled ‘Too big, too small? Too low, too high? Adjuvant choices when stage and biology do not align,’ chaired by Harold Burnstein (USA) and Prudence Francis (Australia). These sessions provided an opportunity for in-depth discussions and critical analysis of the topics, enriching the scientific discourse and contributing to the advancement of breast cancer treatment strategies. Day 3, March 16, 2023, Vienna, Austria On Day 3, a variety of talks focussed on local and systemic approaches. The day began with a discussion on tailoring surgery and radiation, chaired by Jana de Boniface (Sweden) and Lori Pierce (USA). This session explored the selection of the most suitable options for local control and included topics such as patient selection, dose and fractionation for external beam radiotherapy in patients with early breast cancer presented by Charlotte Coles (UK), the benefits and risks of oncoplastic breast-conserving surgery discussed by Marie-Jeanne Vrancken Peeters (The Netherlands), breast surgery after neoadjuvant therapy presented by Andrea V. Barrio (USA) and breast surgery for local recurrence presented by Isabel Rubio (Spain).[18-21] The following session focussed on the controversial topic of axillary management and was chaired by Philip Poortmans (Belgium) and Zhiming Shao (China). Talks in this session covered de-escalation of surgery and radiation, as well as approaches to the postchemotherapy axilla. Topics discussed included the omission of the surgical staging of the axilla presented by Oreste Gentilini (Italy), axillary surgery in the adjuvant setting discussed by Jana de Boniface (Sweden), concepts of limited axillary surgery to determine nodal pathological complete response (pCR) presented by Jörg Heil (Germany) and de-escalation of axillary radiotherapy presented by Icro Meattini (Italy). The highlight of the day was a high-voltage debate titled ‘Axillary dissection versus axillary radiation for residual nodal disease after neoadjuvant systemic therapy’ between Orit-Kaider Person (Israel) and Monica Morrow (USA), which focussed on the management of residual nodal disease in the axilla after neoadjuvant therapy.[22-25] The discussions on systemic therapy continued with lectures on the management of HER2-positive cases, triple-negative cases and options in early breast cancers. A debate titled ‘Need for adjuvant therapy in cases of pCR after neoadjuvant therapy’ was led by Steven Chia (Canada) and Sibylle Loibl (Germany). The day concluded with a debate on whether adjuvant therapy is necessary for patients who achieve pCR after neoadjuvant therapy. This session was chaired by Giuseppe Curigliano (Italy) and Sherene Loi (Australia), and the debaters were Sibylle Loibl (Germany) and Steven Chia (Canada). During session 8, which focussed on optimising treatment in patients with HER2-positive breast cancer, various topics were covered, including assessing HER2 heterogeneity presented by Frederique Penault-Llorca (France), current adjuvant and neoadjuvant approaches discussed by Nadia Harbeck (Germany), emerging new treatments in HER2-positive breast cancer presented by Martine Piccart (Belgium) and addressing the diversity in HER2-positive breast cancer from an ER-positive vs. ER-negative perspective presented by Aleix Prat (Spain).[26,27] Session 9, titled ‘Optimizing treatment in patients with triple-negative breast cancer,’ was chaired by Lisa Carey (USA) and Zefei Jiang (China). The session included discussions on optimal neoadjuvant and adjuvant therapy for patients with early triple-negative breast cancer presented by Hope S. Rugo (USA), optimal systemic therapy for residual disease in triple-negative breast cancer discussed by Sibylle Loibl (Germany), tackling triple-negative histological subtypes in early breast cancer presented by Jorge Reis Filho (USA), and the potential for de-escalating immunotherapy and chemotherapy in triple-negative breast cancer, presented by Hervè Bonnefoi (France).[28-30] The day concluded with a debate on whether adjuvant therapy is necessary for patients who achieve pCR after neoadjuvant therapy. Chaired by Giuseppe Curigliano (Italy) and Sherene Loi (Australia), the debaters Sibylle Loibl (Germany) and Steven Chia (Canada) presented their perspectives on this topic. Overall, day 3 of the conference showcased a wide range of topics related to local and systemic approaches in breast cancer management. The discussions revolved around tailoring surgery and radiation, axillary management, HER2-positive breast cancer treatment optimisation and triple-negative breast cancer treatment strategies. The debates sparked intellectual exchange and provided valuable insights into controversial issues and emerging trends in breast cancer therapy. These discussions contributed to the collective effort to improve patient outcomes and advance the field of breast cancer research and treatment. Day 4, March 16, 2023, Vienna, Austria The final day began with an eye-opening session on the global perspective in breast cancer treatment. Benjamin Anderson from the World Health Organisation shared major insights about similarities and disparities worldwide. The problem statement of breast cancer as a major public health problem worldwide was impressed, and it was abundantly cleared by the data that any public healthcare initiative for cancer should necessarily tackle this problem ahead of most others. The stark difference between cancer treatment outcomes based on resource sufficiency versus resource insufficiency justified the struggle for equitable distribution of resources. This was further expounded by the perspectives from Asia (Binghe Xu, China), Africa (Heba Gamal, Egypt) and Latin America (Denisse Bretel, Peru). The session on endocrine management included discussions on indications for integration of olaparib, adjuvant endocrine options, duration of endocrine treatment and use of neoadjuvant chemotherapy. Debate between Rajendra Badwe (India) and Florian Fitzel (Autria) on the topic of surgery for metastatic disease generated a lot of audience interest in view of clear evidence available from past studies. The crisp summary of literature was received very well. In all the four debates during the congress, the absence of an obvious winner was a testament to the high quality of arguments being presented and a victory of science over prejudice. The most-awaited event of the conference ‘St. Gallen International Consensus Session’ was Chaired by Harold Burnstein (USA) and Giuseppe Curigliano (Italy) and had a large panel comprising opinion leaders from across the globe contributing toward the formulation of guidelines based on meticulously crafted clinical scenario questions and real-world patient interaction situations. The preference of all the panellists was digitally recorded and opened up to audience perusal. The questions were often tuned and even reframed to formulate alternate scenarios to generate discussions on how situational tweaks would alter management choices. The consensus meeting was a profound and comprehensive overview of the open questions in oncology and also an exhibit of how a similar problem would be dealt differently by experts in different parts of the World. This was followed by farewell and announcement of the dates for the 19th St. Gallen Breast Cancer Conference (March 12–15, 2025). HIGHLIGHTS AND CONCLUSIONS The 18th St. Gallen International Breast Cancer Conference 2023 held in Vienna, Austria, brought together experts in breast oncology to discuss advancements and challenges in breast cancer treatment and research. The conference covered a wide range of topics, including local control through surgical and radiation measures, systemic therapy options, immunology, hereditary cancers, adjuvant treatment, and optimisation of HER2-positive and triple-negative breast cancer treatment. The discussions sparked intellectual exchange and provided valuable insights into controversial issues and emerging trends in breast cancer therapy. The consensus session, involving opinion leaders from around the world, formulated guidelines based on real-world patient scenarios, demonstrating how management choices can vary across different regions. Overall, the conference fostered collaboration, shared knowledge, and contributed to improving patient outcomes and advancing breast cancer research and treatment. Moving forward, it is essential to incorporate the key takeaways from the conference into clinical practice and research endeavours. The emphasis on conservative surgeries whenever oncologically feasible underscores the importance of minimising unnecessary mastectomies and reconstructions, ultimately improving the quality of life for breast cancer patients. The discussions on personalised treatment approaches, including genomic risk stratification and targeted therapies, highlight the need for tailored interventions based on individual patient characteristics. Furthermore, the conference shed light on the challenges and opportunities associated with global breast cancer management. The acknowledgment of disparities in treatment outcomes based on resource availability emphasises the urgency of addressing these inequities through collaborative efforts, resource allocation and public healthcare initiatives. The insights shared by experts from different regions of the world provide valuable perspectives on tackling breast cancer as a major public health concern. It is anticipated that the outcomes and insights from the 18th St. Gallen International Breast Cancer Conference will be disseminated widely, both through official publications in a major oncological journal, and through ongoing discussions among the scientific community. The knowledge and lessons gained from the conference will continue to shape the field of breast cancer management, ultimately leading to improved outcomes and enhanced quality of life for patients. In conclusion, the 18th St. Gallen International Breast Cancer Conference provided a valuable platform for knowledge exchange, collaboration and the dissemination of research findings. Acknowledgements The authors would like to express their gratitude for unrestricted research support (Grant no #GC2528) provided by Bajaj Auto Ltd to Prashanti Cancer Care Mission. The authors acknowledge the editorial help provided by Dr. Rupa Mishra and Ms. Jisha John. The authors greatly value the leadership and persistent support of BreastGlobal co-chairs, Dr. Ashutosh Kothari and Prof. Chintamani. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.

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