Routes of Cancer Dissemination: Distinguishing Lymphatic and Hematogenous Spread from Venous Entry to Systemic Arterial Distribution

Background/Objectives: Cancer metastasis is responsible for most cancer-related deaths, yet the precise anatomical and physiological routes by which cancer cells disseminate remain incompletely defined. This review aims to present an integrated model of lymphatic and hematogenous dissemination that provides a unified framework for understanding metastatic progression. Methods: The published literature on lymphatic biology, microvascular physiology, tumor immunology, and cancer metastasis was critically reviewed and integrated to develop a comprehensive anatomical and physiological model of cancer dissemination. Results: The proposed model identifies lymphatic dissemination as the predominant metastatic route in many solid tumors. Cancer cells enter structurally permissive initial lymphatic capillaries and are transported to the sentinel lymph node (SLN), where interactions with the tumor microenvironment may eliminate disseminated cells, maintain dormancy, or facilitate immune escape and further dissemination. Cancer cells that survive within or escape beyond the SLN subsequently travel through collecting lymphatics and the thoracic or right lymphatic duct to enter the systemic venous circulation. Following cardiopulmonary transit, surviving cells may be redistributed through the systemic arterial circulation to distant organs. A secondary pathway involves direct hematogenous intravasation through post-capillary venules, where reduced shear stress, increased endothelial permeability, and permissive endothelial biology facilitate entry into the venous circulation. Thus, lymphatic and direct venular pathways ultimately converge in the venous circulation before systemic arterial dissemination. Conclusions: This unified model integrates lymphatic and hematogenous dissemination into a coherent anatomical and physiological framework. By emphasizing the SLN as an early immunologic checkpoint and the arterial circulation as the final distribution network for disseminated cancer cells, this review provides a conceptual basis for understanding metastatic patterns and identifying biomarkers and therapeutic vulnerabilities.