Single-cell spatial transcriptomics reveals tumor microenvironment heterogeneity in primary and lymph node-metastatic small cell lung cancer.

Lymph node metastasis (LNM) is a critical prognostic and therapeutic determinant in small cell lung cancer (SCLC), yet its spatial cellular ecosystem remains poorly understood. Here, we perform single-cell spatial transcriptomics using the CosMx Spatial Molecular Imager on 105 primary and metastatic lymph node specimens from 75 SCLC patients, generating a comprehensive atlas of over 600,000 cells. We identify three LNM-enriched malignant subclusters with distinct metabolic and angiogenic programs that spatially correlate with immune exclusion features. Spatial analysis reveals vascular-immune crosstalk, wherein endothelial cells orchestrate immune activation through avoidance of malignant cells while forming functional perivascular niches with cytotoxic T cells during LNM. Cellular neighborhood analysis delineates distinct multicellular niches and identifies a pan-immune hotspot (PIHs-1) whose abundance is an independent predictor of survival. This study provides a high-resolution spatial map of the SCLC tumor microenvironment during LNM and establishes spatially defined architectures as both mechanistic insights and translatable biomarkers.