SRS-ICI-radiation-necrosis

SRS × ICI sequencing and radiation necrosis

定義と現象

Stereotactic radiosurgery (SRS) + immune checkpoint inhibitor (ICI) combination は brain metastasis (特に NSCLC / 黒色腫 / RCC) 治療の主流となる一方、(1) radiation necrosis (RN) 増加, (2) pseudoprogression との鑑別困難, (3) abscopal effect vs synergistic efficacy の dual signal が central concern。SRS-ICI sequencing (concurrent vs sequential, ICI-first vs SRS-first) と timing が radiation necrosis incidence を modulate するが、meta-analysis レベルで一貫した optimal protocol は未確立。Brain met-positive NSCLC IO trial (KEYNOTE-189 brain met cohort 等) と SRS practice の cross-talk が clinical decision の central debate。

メカニズム

Radiation necrosis (RN) の増悪 mechanism (under SRS + ICI)

1. Radiation-induced vascular injury: endothelial damage → BBB 破綻 → enhanced inflammation site formation
2. ICI-mediated T-cell infiltration amplification: BBB disruption + IO restoration が CD8 T-cell + microglia の brain met 周囲 inflammation を増幅
3. Astrocyte / microglia reactivity: reactive astrocyte の GFAP 高発現 + microglia M1 polarization で inflammatory edema + fibrinoid necrosis が増加
4. Cytokine storm at irradiated site: TNF-α / IFN-γ / IL-6 高濃度で local damage の sustained inflammation
5. Time course: SRS 後 6-24 か月で発症 peak、ICI 併用で earlier onset / higher incidence (12-30% vs SRS 単独 5-10%)

Pseudoprogression vs true progression vs RN 鑑別

病態	MRI 所見	Time course	Mechanism	臨床対応
True progression	増大 enhancing lesion + perilesional edema	continuous growth	tumor proliferation	switch / local salvage
Pseudoprogression	一過性 enhancement increase	数週-数か月で resolution	ICI-induced immune flare	continue ICI, monitor
Radiation necrosis	central necrosis + peripheral enhancement	SRS 後 6-24 mo	radiation + immune amplification	corticosteroid, bevacizumab, surgery if symptomatic

鑑別補助 imaging: perfusion MRI (rCBV), MR spectroscopy (Cho/Cr ratio), amino acid PET (¹⁸F-FET / ¹¹C-MET), advanced radiomics (foundation model pathology / AI rad)。Final 鑑別は biopsy 必要 case あり。

SRS + ICI の synergy mechanism (positive side)

• Immunogenic cell death (ICD): radiation-induced damage が DAMP (HMGB1, calreticulin) 放出 → DC activation → cross-priming
• Abscopal effect: irradiated site の immune priming が distant unirradiated lesion regression を induce (rare but documented)
• TCR diversity expansion: SRS による neoantigen presentation 増加で TCR repertoire 拡大
• TME 変化: SRS で tumor-resident Treg / MDSC reduction、effector T-cell influx 促進

治療戦略 / 臨床的意義

Sequencing options

• Concurrent SRS + ICI (within 2 weeks): synergy potential 最大、RN risk also 最大
• Sequential ICI → SRS: ICI first で systemic control + tumor priming → SRS で local consolidation
• Sequential SRS → ICI: SRS で local control + neoantigen release → ICI で systemic priming
• Delayed ICI (>4 weeks post-SRS): RN risk 軽減、synergy potential 減
• Driver-positive NSCLC: TKI first (CNS-active TKI sequencing concept で詳述) で IO 不要 case 多

RN 管理

• Asymptomatic small RN: serial imaging, dose reduction
• Symptomatic / large RN:
  • Corticosteroid (dexamethasone) で edema 軽減
  • Bevacizumab (anti-VEGF) が RN 治療で効果的 (Levin 2011 Int J Radiat Oncol; off-label widely used)
  • Laser interstitial thermal therapy (LITT) for refractory / surgical-difficult site
  • Surgical resection if mass effect

Imaging follow-up

• MRI baseline + post-SRS 6w / 3m / 6m / 12m / 24m
• rCBV, ADC で early necrosis prediction
• ¹⁸F-FET PET 鑑別 (if available)

Trial design

• Brain met cohort を IO trial の standard sub-group に組込み (KEYNOTE-189, CheckMate-9LA, POSEIDON 等)
• Stratification factors: SRS history, brain met count / size, leptomeningeal disease
• CNS endpoint: intracranial PFS, time to neurologic event, neurocognitive function

Open Questions

• Optimal SRS + ICI sequencing: prospective dedicated trial (NRG-CC003 等)
• RN biomarker: pre-SRS imaging / blood biomarker で high-risk patient identification
• Anti-VEGF (bevacizumab) prophylaxis for high-risk patient
• RN incidence under bispecific / ADC + SRS: novel modality 時代の未検証 area
• Driver-positive (EGFR / ALK) brain met での SRS + IO 適応 (mostly TKI 単剤で十分 case 多)
• AI-driven RN vs progression discrimination: foundation model imaging の clinical translation
• Brain met clonal evolution と SRS / IO sequencing の interaction

関連エンティティ・概念

• 関連細胞: Astrocyte / Reactive-astrocyte / Microglia / Border-associated-macrophage / CD8-T-cell / Endothelial-cell / Pericyte
• 関連薬剤: PD-1-inhibitor / PD-L1-inhibitor / CTLA-4-inhibitor / anti-VEGF-antibody / Corticosteroid / Osimertinib / Lorlatinib / Tucatinib
• 関連サイトカイン: TNF-alpha / IFN-gamma / IL-6 / VEGF / HMGB1
• 関連経路: BBB-neurovascular-unit-pathway / Interferon-pathway / NF-kB-pathway / VEGF-angiogenesis-pathway
• 関連手法: Radiomics / Foundation-model-pathology / Tissue-clearing-3D-imaging / Multiplex-IF-imaging / ctDNA-liquid-biopsy
• 関連概念: Brain-metastasis-immune-microenvironment / BBB-disruption-in-brain-metastasis / Leptomeningeal-metastasis / CNS-active-TKI-sequencing / Brain-metastasis-clonal-evolution / Reactive-astrocyte-tumor-crosstalk / Abscopal-effect / Immunogenic-cell-death / irAE-pathophysiology

関連論文

Basic-Brain metastasis

• Mavrikios et al. AnnOncol 2026 — Lung cancer brain metastases management at the dawn of personalized medicine are we ready to break the barriers
• Eguren-Santamaria et al. ClinCancerRes 2020 — PD-1pd-L1 blockers in NSCLC brain metastases challenging paradigms and clinical practice
• Chen et al. FrontOncol 2026 — Stereotactic radiotherapy for brain metastases indications, dose fractionation, technological innovations, and evolving

Basic-Extracellular vesicles

• Veerappan et al. AmJPhysiolLungCellMolPhysiol 2016 — Mast cells and exosomes in hyperoxia-induced neonatal lung disease
• Escola et al. JBiolChem 1998 — Selective enrichment of tetraspan proteins on the internal vesicles of multivesicular endosomes and on exosomes
• Hsu et al. JCellBiol 2010 — Regulation of exosome secretion by rab35 and its GTPase-activating proteins TBC1D10A-C
• Raiborg et al. JCellSci 2001 — FYVE and coiled-coil domains determine the specific localisation of Hrs to early endosomes
• Raposo et al. JExpMed 1996 — B lymphocytes secrete antigen-presenting vesicles
• Arvanitaki et al. ProcNatlAcadSciUSA 2024 — Microglia-derived extracellular vesicles trigger age-related neurodegeneration upon DNA damage

Basic-Immunotherapy

• Im et al. Nature 2016 — Defining CD8+ T cells that provide the proliferative burst after PD-1 therapy
• Sahin et al. Nature 2017 — Personalized RNA mutanome vaccines mobilize poly-specific therapeutic immunity against cancer

Basic-Liquid-biopsy

• Horndalsveen et al. JThoracOncol 2026 — ctDNA based MRD detection in stage III NSCLC treated with chemoradiotherapy and durvalumab

Basic-Others

• Kebriaei et al. JClinInvest 2016 — Phase I trials using sleeping beauty to generate CD19-specific CAR T cells

Clinical-NEC

• Steuer et al. JThoracOncol 2015 — Atypical carcinoid tumor of the lung a surveillance, epidemiology, and end results database analysis

Clinical-NSCLC-Driver negative

• Fossella et al. JClinOncol 2000 — Randomized phase III trial of docetaxel versus vinorelbine or ifosfamide in patients with advanced non-small-cell lung
• Gronberg et al. JClinOncol 2009 — Phase III study by the norwegian lung cancer study group pemetrexed plus carboplatin compared with gemcitabine plus
• Goldberg et al. LancetOncol 2020 — Pembrolizumab for management of patients with NSCLC and brain metastases long-term results and biomarker analysis from

Clinical-Novel modalities

• Bajgain et al. CellRepMed 2026 — Engineering functionality-optimized fully human B7-H3 CAR T cells for enhanced solid tumor therapy
• Strauss et al. ClinCancerRes 2018 — Phase I trial of M7824 (MSB0011359C), a bifunctional fusion protein targeting PD-L1 and TGFbeta, in advanced solid

Clinical-Supportive care

• Roeland et al. JClinOncol 2020 — Management of cancer cachexia ASCO guideline

Clinical-Thymic

• Rajan et al. JImmunotherCancer 2019 — Efficacy and tolerability of anti-programmed death-ligand 1 (PD-L1) antibody (avelumab) treatment in advanced thymoma

合成 (Outputs)

• brain-metastasis-srs-io-sequencing