Tips-21 phase i/ii study of stereotactic radiosurgery with concurrent olaparib followed by adjuvant durvalumab and physician’s choice systemic therapy in subjects with breast cancer brain metastases (solara)

Abstract BACKGROUND Despite progress in the treatment of brain metastasis (BrM) for HER2+ breast cancer (BC), outcomes for patients with HER2-negative BC BrM remain poor. Current standard of care consists of surgery and/or radiotherapy followed by systemic therapy. Preclinical studies show inhibitors of poly(ADP-ribose) polymerase (PARP) are effective together with radiotherapy as DNA damage response inhibitors. Triple-negative BC (TNBC) has higher rates of homologous recombination deficiency compared to other BC subtypes, and together with HER2-negative, BRCA-mutated BC would be particularly sensitive to PARP inhibition. PARP inhibition with immunotherapy has demonstrated promising efficacy in patients with germline BRCA-mutant and metastatic TNBC in clinical trials (MEDIOLA, TOPACIO). In addition, immunotherapy with stereotactic radiosurgery (SRS) is associated with favorable outcomes in patients with BrM. We hypothesize that this biologically-driven combination will enhance local control of SRS-treated BrM through synergy with PARP inhibition, while controlling micrometastatic disease in the brain and extracranial sites by potentiating the immune response. METHODS We are conducting a multi-institution, Phase I/II trial of SRS plus olaparib, followed by durvalumab (with physician’s choice systemic therapy), for patients with TNBC (any BRCA status) or HER2-negative with BRCA-mutated (germline or somatic) BC BrM [NCT04711824]. The primary objectives are to evaluate safety and tolerability (Phase I) and intracranial disease control at 6 months (Phase II). Secondary objectives include assessing intracranial and global progression-free survival, overall survival, and intracranial/extracranial response rate. Exploratory objectives will assess potential biomarkers of treatment response, including changes in circulating tumor cells/DNA in blood and cerebrospinal fluid, germline and tumor mutations in DNA repair pathway genes, and PD-L1 expression, as well as quality of life and patient-reported outcomes. A surgical sub-study (n=5) will evaluate olaparib concentration/distribution in resected BrM. As of January 2023, cohort 1 of phase I has been completed without dose-limiting toxicity.