Lymphatic Transport and Lymph Node Location of Microspheres Subcutaneously Injected in the Vicinity of Tumors in a Rabbit Model of Breast Cancer.

Purpose: To assess the lymphatic transport of microparticles of 100 nm, 1 μm and 10 μm subcutaneously injected into the breast area of healthy and tumor-bearing rabbits, and to analyze their location in lymph node (LN) in relation to malignant cells.
Methods: Female rabbits (n = 9) bearing a VX2 tumor in one thoracic mammary gland were subcutaneously injected at D15 with polystyrene fluorescent particles around the nipple, on the tumor and on the healthy sides. The tumor and the LN measured by ultrasound at D9, D15 and D20 were explanted at D20. The LN metastases were evaluated by cytokeratin staining. LN uptake of the particles was measured by quantifying the green fluorescence surface in hot spot regions of healthy and pathologic LN.
Results: All animals developed mammary tumors. Metastases were found in 39% of LN from the tumor side. LN invasion was significantly lower for the 10 μm group versus the 100 nm group (p < 0.0348). The fully invaded area of metastatic LN contained significantly less 100 nm and 1 μm particles compared to the low and non-invaded regions and to the healthy LN. In the invaded LN, the 1 μm MS occupied more surface than the 100 nm particles.
Conclusions: 1 μm MS arrived numerously into the areas low-invaded and non-invaded by the tumoral cells of the pathologic LN, but they were very rare in the fully invaded regions. Compared to the 100 nm nanospheres, the 1 μm were better retained (20 times) into the sentinel LN, showing the advantage of micrometric particles for lymph-targeted chemotherapy when injected before complete invasion by metastases.