Figure 3. The mouse ear sponge model recapitulates the primary tumor growth, pre-metastatic and metastatic stages in LNs.

Sponges soaked with serum-free DMEM medium (control condition without tumor cells), 1.5 × 10⁵ or 2 × 10⁵ B16F10Luc+ cells diluted in serum-free DMEM medium, were implanted into both C57BL/6J mouse ears and mice were kept for 2 or 4 weeks. (a) Representative pictures showing the in vivo bioluminescent signals of the primary tumors developed in ears, at 2 (left panels) and 4 (right panels) weeks post-sponge insertion. Numeric values depicted in the color scale for the radiance are expressed in photons/sec/cm². (b) Quantification of bioluminescent signal radiance expressed in photons/sec/cm² and measures of tumor sizes from histological sections of ear sponges. Data are presented as mean ± SEM, Wilcoxon-Mann-Whitney significance test was used to compare the mean parameter values, *p < 0.05, **p < 0.01, ***p < 0.001, n = 12 sponges per group (6 mice/group). (c) Representative pictures of ex vivo bioluminescent signal of the draining sentinel LNs at week 2 (left panels) and 4 (right panels) post-sponge implantation. Numeric values displayed in the color bar for radiance are expressed in photons/sec/cm². For positive LNs, a bright field picture of LN is shown below the bioluminescent images. (d) Table of positive LNs incidence at week 2 and 4 post-sponge insertion. “L” represents left mouse ear/LN and “R” refers to right mouse ear/LN, n = 12 LNs per group (6 mice/group).