ESTRO 2024 - Abstract Book

S692

Clinical - Breast

ESTRO 2024

Results:

Data of 52 consecutive patients treated with T-DXd with or without RT were retrospectively evaluated. Sixteen patients received RT immediately before (within a month) or during T-DXd, for a total of 17 RT treatments, while 36 patients did not. Median age was 54 years old (range 34-88). At a median follow up of 6 months (range 1-24), 3 patients (18.8%) had died in the RT group, while 5 patients (13.9%) in the no-RT group. Twenty-one patients (40.4%) received T-DXd as fourth or further line of systemic anti-HER2 treatment, while 16 (30.8%) in third line and 13 (25.0%) in second line. Two patients (3.8%) with early metastatic disease relapse (<6 months after adjuvant anti HER2 therapy completion) received T-DXd as first line treatment. Median total RT dose prescription was 30 Gy (range 8-48) with a median number of fractions of 3 (range 1-15). Median EQD2 dose was 50 Gy (range 16-104) and median BED 60 Gy (24-149). The most frequently treated site was bone (47.1% of cases; N=8/17) followed by brain (29.4%; N=5/17). A chi-square test of independence was performed to examine the relation between RT administration and the development of >G2 toxicity. The relation between these variables was not significant (p = 0.83). Regarding toxicities of special interest for T-DXd, 3 cases of G3 fatigue have been reported in no-RT group with 1 case in the RT group. Overall, only 1 case of G3 nausea was observed (in the no-RT group). Grade 2 interstitial lung disease (IDL), that led to T-DXd discontinuation, was observed in 1 case in RT group and in 2 cases in no-RT group. No radionecrosis events were observed among the 4 patients treated with intracranial RT.

Conclusion:

Our first data are encouraging regarding the potential safety of this combination, showing that concurrent RT did not increase severe acute toxicity. Data from larger series are needed to confirm these results.

Keywords: Trastuzumab deruxtecan, radiotherapy, combination

2893

Digital Poster

Impact of radiation therapy for primary tumor in de novo metastatic breast cancer patients

Raouia Ben Amor 1,2 , Ferdaous Friaa 1,2 , Zeineb Naimi 1,2 , Ines Mlayah 1,2 , Ghada Abdessatar 1,2 , Awatef Hamdoun 1 , Lotfi Kochbati 1,2 1 Abderrahmane Mami Hospital, Radiation Oncology, Ariana, Tunisia. 2 Faculty of Medicine Of Tunis, University of Tunis El Manar, Tunis, Tunisia

Purpose/Objective:

the value of locoregional treatment (LRT) of the primary tumor in de novo metastatic breast cancer (dNMBC) patients and its impact on survival still under debate, with very few data available regarding exclusive radiotherapy