ESTRO 2025 - Abstract Book

S498

Clinical - Breast

ESTRO 2025

Results: 129 patients were included: 99 (77%) had hormone receptor-positive/HER2-negative (HR+/HER2-) disease and 11 (9%) patients had visceral OPD; bone and lymph nodes represented oligoprogressive sites in 94 (73%) and 28 (22%) patients, respectively. Median pRT-PFS was 11.3 months (95%CI, 9.1-13.5) and median NEST was 13.6 months (95%CI, 11.5-15.2). Only 19 (15%) patients experienced a subsequent PD in the OPD sites treated with SBRT. In the HR+/HER2- mBC subgroup, the median pRT-PFS and NEST were 11.5 months (95%CI, 8.5-13.4) and 14.2 months (95%CI, 11.6-18.3). Conclusion: Patients with mBC, especially with HR+/HER2- disease and experiencing non-visceral OPD, seem to benefit from OPD-directed SBRT without changing systemic treatment, suggesting its broader implementation in clinical practice.

Keywords: breast, oligometastasis, stereotactic radiotherapy

1884

Digital Poster Comparative efficacy and safety of two radiotherapy protocols for ovarian ablation in metastatic breast cancer patients Tasneem Hossain 1 , Erika Galietta 2,3 , Alessio Giuseppe Morganti 2,3 , AFM Kamal Uddin 4 , Shahida Alam 1 , Altaf Hossain 5 , Sonya Begum 6 , Qazi Mushtaq Hussain 7 , Silvia Cammelli 2,3 , Arina Alexandra Zamfir 2 , Ludovica Forlani 3 , Nowshin Taslima Hossain 8 1 Radiation Oncology, National Institute of Cancer Research and Hospital, Dhaka, Bangladesh. 2 Radiation Oncology, IRCCS Azienda Ospedaliero-Universitaria di Bologna, Bologna, Italy. 3 Radiation Oncology, Department of Medical and Surgical Sciences (DIMEC), Alma Mater Studiorum - Bologna University, Bologna, Italy. 4 Radiation Oncology, National Institute of ENT, Dhaka, Bangladesh. 5 Radiation Oncology, Khulna Medical College and Hospital, Khulna, Bangladesh. 6 Oncology, Delta Hospital Limited, Dhaka, Bangladesh. 7 Clinical and Radiation Oncology, Labaid Cancer and Superspeciality Centre, Dhaka, Bangladesh. 8 Radiation Oncology, Ahsania Mission Cancer and General Hospital, Dhaka, Bangladesh Purpose/Objective: This study aimed to evaluate the efficacy and safety of radiotherapy (RT) for ovarian ablation (OA) in metastatic breast cancer patients, comparing two RT protocols: 15 Gy in 5 fractions (arm A) versus 20 Gy in 10 fractions (arm B). Material/Methods: Conducted at the National Institute of Cancer Research and Hospital, Dhaka, the study enrolled 68 patients, divided equally into two arms. They were followed up for 24 weeks post intervention. The primary endpoint was the efficacy of RT in inducing OA, assessed through amenorrhea and hormone levels (FSH and Estradiol). Toxicities were evaluated using the Common Toxicity Criteria for Adverse Events version 5.0, and post-menopausal symptoms were assessed with the Menopause Rating Scale. Results: There was no significant difference between the two arms (A vs. B) in the rate of amenorrhea development and persistence (85.7% vs. 89.5%), achievement of postmenopausal Estradiol (91.2% vs. 94.1%), and FSH levels (79.4% vs. 88.2%). Both regimens showed a significant reduction in Estradiol and increase in FSH levels compared to baseline. No grade ≥3 toxicity was observed. Common postmenopausal symptoms included hot flushes and irritability, with no significant difference between the groups.