Abstract B067: The Melanoma CTC Brain-Liver Metastasis Axis

Abstract Melanoma brain metastasis (MBM) is linked to dismal prognosis and onset of brain metastasis is increasing in frequency in all cancer types. Circulating Tumor Cells (CTCs) are "seeds" of fatal metastasis and smallest functional units of cancer. We previously employed an unbiased, multipronged approach to discover a unique ribosomal protein large/small subunit (RPL/RPS) CTC gene signature associated with MBM. In this study, we hypothesized that MBM-CTC drives secondary metastasis (“metastasis of metastasis” per clinical scenarios), and has targeted organ specificity for the liver. We injected parallel cohorts of immunodeficient and newly developed humanized NBSGW (huNBSGW) mice with cells from CTC-derived melanoma brain metastasis to identify secondary metastatic patterns. We found the presence of a melanoma brain-liver metastasis axis in huNBSGW mice. Furthermore, RNA sequencing analysis of tissues showed a significant upregulation of the RPL/RPS CTC gene signature linked to metastatic spread to the liver. Additional RNA sequencing of CTCs from huNBSGW blood revealed extensive CTC clustering with human B cells in these mice. CTC:B-cell clusters were also upregulated in the blood of patients with primary melanoma and maintained either in CTC-driven MBM or MBM CTC-derived cells promoting extensive liver metastasis. CTC-generated tumor tissues were interrogated at single-cell gene and protein expression levels (10x Genomics Xenium and HALO spatial biology platforms, respectively). Collectively, our findings suggest the presence of a CTC brain-liver metastasis axis, and that heterotypic CTC:B-cell interactions can be critical at multiple stages of metastasis. Significance: This study provides important insights into the relevance of prometastatic CTC:B-cell clusters in melanoma progression, extends the importance of the CTC RPL/RPS gene signature beyond primary metastasis/MBM by driving targeted organ specificity for liver metastasis (“metastasis of metastasis”), and identifies new targets for therapies against clinical melanoma metastasis, eg, ongoing studies involcving cryogenic electron microscopy analyses of CTC ribosomes. Citation Format: DARIO MARCHETTI. The Melanoma CTC Brain-Liver Metastasis Axis [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Brain Cancer; 2026 Mar 23-25; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2026;86(6_Suppl):Abstract nr B067.