Single-cell RNA sequencing reveals cellular and molecular heterogeneity in extensive-stage small cell lung cancer...

Despite its rapid growth and early metastasis, small cell lung cancer (SCLC) is more chemosensitive than other lung cancers. However, some patients with extensive-stage SCLC (ES-SCLC) do not respond to first-line chemotherapy, resulting in poorer prognoses due to inter- and intratumoral heterogeneity. In this study, we conducted single-cell RNA sequencing of 9 treatment-naive ES-SCLC samples. Based on comprehensive imaging evidence collected before and after two cycles of first-line chemotherapy and sample types, the 9 samples were categorized into three groups: progressive disease with the pleural effusion sample (PD_PE group, n = 1), progressive disease with the primary tumor samples (PD_TU group, n = 2), and partial response with the primary tumor samples (PR_TU group, n = 6). Based on transcriptomic landscape and cell type composition, the PD samples represent a multicellular ecosystem distinct from PR samples. The immune response, along with the elevated expression of immune-related genes such as LTF, SLPI, SPARC and IGLV1-51, might correlate with a poor first-line chemotherapy response in ES-SCLC. We also observed that T cells, particularly effector T cells, were more abundant in PD_TU group, with TNFA signaling via NFκB being significantly enriched. The PD_TU group was strongly enriched with macrophages and tumor-associated macrophages (TAMs), and angiogenesis in TAMs was highly enriched. Immunomodulatory fibroblasts were highly abundant in PD_TU group, and the pathways of epithelial-mesenchymal transition and angiogenesis were upregulated. This study offers the first comprehensive insights into the cellular and molecular heterogeneity in treatment-naive patients with ES-SCLC with different chemotherapy responses.