Bonghan Ducts as Possible Pathways for Cancer Metastasis

Visualization of the Bonghan system on the fascia surrounding tumor tissue in the skin of a mouse. (A) Images of tumor tissue, indicated by arrows; left: a mouse with two tumors, grown for two weeks after subcutaneous inoculation; right: tumor tissue surface after skin sectioning; Bonghan system hardly detectable. (B) In situ trypan blue staining of ducts (dotted arrows) and corpuscles (arrow heads) on fascia surrounding tumor tissue; right panel, magnified view of left panel; trypan blue did not stain blood vessels. (C) Multiple ducts (dotted arrows) on fascia surface of tumor tissue; right panel, magnified view of left panel; branching of duct and duct enters nearby fat layer (double arrow). (D) Trypan blue technique revealed Bonghan ducts (dotted arrows) along bundle of blood vessels and nerves; right panel, duct along blood vessel; bundle of blood vessels and nerves connect tumor tissue (an arrow) at lower left corner to outside skin. Samples A, B, C, and D from different mice.

Photomicrographs of cross-sections of Bonghan duct found on the surface of solid mouse tumor with H&E staining. Sample of Figure 1B. (A) Duct (double arrow) located on fascia (dashed arrows) covering solid tumor. (B) Pho tomicrograph showing several ductules (arrow) in duct, in both cross- and oblique-sections; flowing cells (arrowhead) with round or oval nuclei observed in some duct lumina; nuclei in lumen endothelial cells. (C, D) Duct histological characteristics; high magnification; W, wall of the ductule; arrow and arrowhead, ductule and flowing cells in lumen, respectively. Magnifications: A, 100×; B, 400×; C and D, 1,000×.

Photomicrographs of Bonghan corpuscle cross-sections. Sample from Figure 1B. (A) Light microscope image of general corpuscle histology. (B-D) Magnified images of Figure 3A; presence of many ductules (arrow) in corpuscles, appear in cross- and oblique-sections; ductule diameter from 5-50 μm; parts of corpuscle boundary surrounded by external connective tissue membrane (arrow heads); parts not (asterisks). Magnifications: A, 200× and B-D, 400×.