LOCL-12 OUTCOMES OF STEREOTACTIC RADIOSURGERY FOR BRAIN METASTASES OF BREAST CANCER IN RELATION TO MOLECULAR SUBTYPES. (5th August 2022) - Andreasen, Lærke Wolf
Abstract: PURPOSE: To determine intracranial outcomes following stereotactic radiosurgery (SRS) for brain metastases of breast cancer in relation to molecular subtypes of HER2 (human epidermal growth factor receptor) overexpression and estrogen receptor (ER) expression. METHOD: From a retrospective institutional database of SRS using VMAT (volumetric modulated arc therapy) carried out between 2012 and 2019, patients with a primary diagnosis of breast cancer were identified. Outcomes following first course of SRS were analyzed using radiotherapy plans and electronic patient records. Systemic anticancer treatments were not registered. Time to intracranial progression (TTP) was calculated using the Kaplan Meier method as the time between SRS and recurrence, whereas dates of death or last follow up without recurrence were censored. The study was approved by the Danish Patient Safety Authority (nr. 31-1521-125). RESULTS: The study included 159 patients. 132 patients (83%) underwent a brain MRI examination after SRS and, of these, 101 had recurrence, either local (41%), remote (43%) or both (16%). Tumors were HER2 positive in 50% of cases and 61% were ER positive and 15% were triple negative. The median intracranial TTP was for the whole study group 9.1 months. Median intracranial TTP for patients with the HER2+ / ER+ subtype was 15.4 mos. whereas patients with the triple negative subtype had a significantly shorter median intracranial TTP of 5.1 mos. (p=0.007). Patients with HER2+/ER- and HER2 normal/ER+ had similar median intracranial TTP times of 7.7 mos. and 8.4 mos., respectively (n.s.). CONCLUSION: This study found high rates of intracranial recurrence following SRS and poor intracranial TTP that was highly dependent on molecular subtypes, reflecting either biological differences or intracranial effect of systemic treatments or both. The study confirms the universally poor prognosis for breast cancer patients with brain metastases and the high frequency of HER2 overexpression in this patient group.