Tumor-intrinsic IFNγ signaling and niche adaptation drive early colonization in ovarian cancer metastasis.

The mechanisms enabling disseminating tumor cells to survive and colonize peritoneal niches during ovarian cancer metastasis remain incompletely understood. Here, we present MetTag, a single-cell barcoding and transcriptome profiling approach with time-stamped batch identifiers to resolve temporal dynamics of dissemination. Sequencing of MetTag barcodes reveals enrichment of early-disseminated clones across metastatic sites, and targeted depletion of pioneers diminishes the outgrowth of later arriving cells. MetTag-coupled single-cell RNA sequencing uncovers a distinct interferon-gamma-centric transcriptional trajectory enriched among pioneer clones. CRISPR/Cas9 screening and subsequent interferon-gamma receptor 1 knockout in pioneer cells significantly reduces metastatic burden, highlighting a critical window where active interferon-gamma signaling shapes the post-seeding metastatic niche and outgrowth. Mechanistically, the tumor-intrinsic interferon-gamma response and peritoneal macrophages cooperatively shield disseminating tumor cells from anoikis. Our study defines the temporal clonal architecture of peritoneal metastasis, revealing a first come, first served dissemination principle, where pioneer fitness determines the success of subsequent colonizers.