Abstract CT204: Efficacy of Bria-IMT regimen in inducing CNS metastasis regression

Abstract Objectives: Breast cancer metastasis to the central nervous system (CNS) often leads to severe morbidity and mortality, and while systemic treatments manage primary tumors, their impact on CNS metastases is limited. This retrospective analysis evaluates the efficacy of Bria-IMT as a monotherapy or in combination with an immune checkpoint inhibitor (ICI) on CNS tumor regression. Methods: Post-hoc analysis of a subset of advanced MBC patients with CNS metastases from previous phase 1 and 2, and ongoing randomized phase 2 trials involving SV-BR-1-GM. SV-BR-1-GM is a GM-CSF secreting, antigen-presenting immortalized breast cancer cell line. Bria-IMT (SV-BR-1-GM ~20x106 cells, intradermally 48-72 hours after cyclophosphamide 300 mg/m2, followed by interferon-alpha at the inoculation sites 2 days later) was administered q3wks. In the combination setting, an ICI was administered with each cycle. Patients A002 and 02-003 received Bria-IMT as monotherapy. Patients 06-005 and 06-007 received Bria-IMT in combination with an ICI. Results: Median pt age of 65 (range 58-70). All pts had ≥1 HLA match with SV-BR-1-GM. Significant CNS tumor regression was observed in all pts. Pt A002 (ER+/PR+, HER2-) received 6 cycles, achieving an 83% reduction in breast lesions. ~3 months after the last cycle, imaging revealed the onset of multiple brain metastases and recurrence of right breast lesions. Following 3 additional cycles, marked measurable regression in both brain metastases and breast lesions was noted. Pt 02-003 (ER-/PR-, HER2 1+ (IHC) ) received 5 cycles and observed a 60% reduction (5mm -2mm) in a left parietal periventricular lesion, and complete resolution (CR) of a left parietal lobe lesion. Pt 06-005 (ER+/PR-, HER2 1+ (IHC) ) demonstrated a 56% (9mm - 4mm) reduction in the thickness of a dural lesion overlying the left anterior temporal lobe after 6 cycles of SV-BR-1-GM + ICI (pembrolizumab). After 2 additional cycles of SV-BR-1-GM + ICI (retifanlimab) and 1 cycle of SV-BR-1-GM (ICI was skipped on final cycle due to grade 2 AE), patient achieved CR of a left orbital mass observed at baseline (24mm - 0m). Circulating cancer-associated macrophage-like cells (CAMLs) varied throughout the treatment, with levels ranged from a baseline of 90 to 24 by Cycle 13. Pt 06-007 (ER-/PR-, HER2 1+ (IHC) ) demonstrated significant reductions in CNS lesions after 3 cycles of SV-BR-1-GM + ICI (pembrolizumab): a 67% reduction in a right frontal lobe lesion, 29% in the right parietal, 30% in the right thalamus, and 67% in the right precentral gyrus lesions. CAML levels remained low throughout treatment. Conclusions: This review consolidates evidence for the efficacy of the Bria-IMT regimen in CNS metastasis regression, both alone and with ICIs. The consistent regression seen across all breast cancer subtypes among heavily pretreated patients highlights the potential of SV-BR-1-GM in managing CNS metastasis. Ongoing trials will determine the full extent. Citation Format: Sailaja Kamaraju, Blaise Bayer, Mingjin Chang, William Williams, Charles Wiseman, Giuseppe Del Priore. Efficacy of Bria-IMT regimen in inducing CNS metastasis regression abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (7Suppl): Abstract nr CT204.