ESTRO 2024 - Abstract Book

S584

Clinical - Breast

ESTRO 2024

A total of 26 pts with HER2-positive MBC were treated for brain metastasis at our institution (Table 1). The median age was 51 years [range 31-81 years]. Seventeen pts received single fraction (15-24Gy) stereotactic radiosurgery (SRS) and 3 pts received hypofractionated (25Gy in 5 fractions) SRS. Gamma Knife-SRS, CyberKnife-SRS and Volumetric Modulated Arc Therapy (VMAT) were performed in 9 (34%), 7 (27%) and 4 (15%) pts. Six out of 26 (26%) pts underwent Whole Brain RT (WBRT). The median time interval between T-DM1 administration and RT (SRS/WBRT) was 16 days [range 3-27 days]. The median PFS from the first course of SRS/WBRT was 13 months [95% CI 7,5-18,5 months], whereas the median OS was not reached (Figure 1a). The 1- and 2-year LC of brain lesions treated with SRS were 83% and 75%, respectively (Figure 1b). Out of 20 pts treated with SRS, 4 had acute toxicity: grade (G) 1 amnesia (1pt), G2 visual deficit (1 pt), G2 dizziness (1 pt), G2 brain oedema (1 pt). Only 1 pt (4%) experienced G3 radionecrosis after 8 months from SRS, requiring hospitalization and corticosteroid treatment. No chronic side effects were observed. One pt receiving WBRT, reported G2 brain oedema one month after RT.

Conclusion:

To date, there is still a lack of prospective studies investigating the safety of combination between T-DM1 and intracranial RT. Hence, caution is advised when combining T-DM1 with RT for brain metastasis.