Organotropism-specific circulating tumor cells profiles: Morphology and heterotypic clustering predict metastatic sites in liquid biopsy of solid tumors

Background: While circulating tumor cells (CTCs) are the primary drivers of metastatic dissemination, the mechanisms governing their organotropism remain poorly characterized. CTC morphology, including size and elongation, and cluster configuration (homotypic vs. heterotypic) may encode site-specific metastatic signatures. Characterizing these features could provide critical pre-radiological biomarkers for predicting organ-specific recurrence and refining metastatic risk assessment in clinical. Methods: We analyzed a large retrospective cohort of patients with a single metastatic site (bone, liver, brain, or lung), regardless of primary tumor origin, using the CellSearch® system. CTC were classified by morphological subtypes (canonical, large, elongated) and cluster phenotypes (homotypic versus heterotypic). Results: CellSearch® profiling of 8359 CTCs from 82 patients with metastatic cancer uncovered marked site-specific heterogeneity reflective of tumor burden and biological tropisms. Among 34 patients with bone metastases, 7010 CTCs (median 21 [IQR 6-135]) were predominantly canonical (85%) and organized in nearly exclusive homotypic clusters (97.7%). In 26 patients with liver metastases, 1273 CTCs (median 4 [IQR 3-7]) shifted to large CTCs (80%) with mixed homotypic (65.2%) and heterotypic (34.8%) clustering. Conversely, 22 patients with brain/lung metastases yielded 76 CTCs (median 3 [IQR 3-5]), enriched for elongated forms (84%) in exclusively heterotypic clusters (100%). These distinct profiles demonstrated statistically significant disparities (P < 0.001), implicating anatomical and microenvironmental drivers of CTC shedding and dissemination. Conclusions: CTC morphology and heterotypic clustering exhibit organotropism-specific profiles, aligning with microenvironmental cues like capillary shear, endothelial activation, and immune niches. These findings position multimodal CTC analysis as a liquid biopsy tool for early metastasis site forecasting, guiding precision interventions.