Immune remodelling and molecular profiling of progressive brain metastases following cranial radiotherapy.

PURPOSE: Given the early recurrence of brain metastasis (BM), identifying factors that drive BM progression is of clinical interest. This study investigates genetic, epigenetic, and inflammatory signatures in progressive BM following different therapeutic approaches.

METHODS

A total of 153 patients who underwent surgical resection for progressive BM were grouped according to the therapeutic strategies prior to the first BM resection: prior radiation (n = 43), systemic therapy (n = 37), combined radiation and systemic treatment (n = 10), and treatment-naive patients (n = 63). Among the treatment-naive patients, 35/63 (55.5%) experienced another intracranial relapse and underwent a second resection (=relapse group), enabling paired analyses. Of these, 23/35 (65.7%) received no therapy between resections; 12/35 (34.3%) received CNS-directed radiotherapy. Tissue samples were analysed using whole-exome sequencing, DNA methylation profiling, and immunohistochemistry.

RESULTS

BM resected after progression following prior cranial radiotherapy (43/153, 28.1%) showed significantly lower densities of CD3 + , CD8 + , and CD45RO + cells together with increased FOXP3 + cell density compared with treatment-naïve BM (63/153, 41.2%; median CD3 +: 71 vs. 494 cells/mm²; CD8 +: 44 vs. 187 cells/mm²; CD45RO+: 104 vs. 302 cells/mm²; FOXP3 +: 215 vs. 41 cells/mm²). In the paired analyses, progressive specimen after prior radiation were likewise associated with significantly reduced CD3 + , CD8 + , and CD45RO + and increased FOXP3 + cell densities compared with the matched baseline specimen. In contrast, no genetic alterations or differences in DNA methylation patterns between irradiated and non-irradiated matched samples were identified.

CONCLUSION

Progressive BM following cranial radiotherapy demonstrated a distinct immune marker profile consistent with a more immunoregulatory, rather immunosuppressive tumour microenvironment. No therapy-associated genetic or epigenetic alterations were identified. Further prospective studies are warranted to determine whether these immune alterations reflect treatment-related effects or biological features associated with resistance following radiotherapy.