Weight increased fivefold in this SLN relative to untreated controls (Figure 2C). SLN enlargement began 1 day after melanoma cell inoculation. These results implied that before metastasis, SLNs show tumor-reactive lymphadenopathy. Histologically, enlarged SLNs showed remarkable medullary hyperplasia (Figure 2D). The hyperplastic medulla consisted of an increased number of lymphatic sinuses of increased dilatation (Figure 2E) that contained few lymphocytes and macrophages. Figure 2 Non-metastatic cervical sentinel lymph nodes in oral melanoma-bearing mice. (A) Detection of a sentinel lymph node (SLN), showing remarkable enlargement, by injection of Evan’s blue dye. In

contrast, contralateral LN (CLN) is also stained with dye, but shows no enlargement. (B) Photograph of an click here enlarged SLN (arrow) on the left side of the cervix and a normal-like CLN (arrowhead). (C) LN weight is significantly increased in nonmetastatic SLNs relative to control, non-draining LNs as determined by t-test. *, P<0.05. Columns, mean; bar, standard error. (D), (E) Light micrographs of hematoxylin and eosin staining in SLNs. At a lower magnification (D), remarkable enlargement of the medulla (Me) is noted. Dilated sinuses (MeS) are clearly visible in the Me of SLNs (E). ALV, afferent lymphatic vessels; SS, subcapsularsinuse; Co, Cortex; LyN, lymphatic nodule; MeC, medullary cord. Scale bars = 50 μm. Tumor-bearing

SLNs Next, we examined pathological changes in tumor-bearing SLNs. In this model, LN metastases were detected 2 days after inoculation (Figure 3A). By 12 days, rates of metastasis exceeded selleck chemical 90%. Most mice died before 21 days because of eating disorder caused by enlarged tumor of the tongue [21]. Tumor metastasis was indicated macroscopically by the deposition of melanin in SLNs, in addition to LN enlargement

(Figure 3B). After 10 days, some tumor-bearing mice possessed bilateral metastases in cervical LNs (Figure 3C). To elucidate the patterns of invasive patterns of tumor cell invasion into SLNs [22], we analyzed HE-stained sections of nodes (Figure 3D). On day 2 and day 3, most LNs revealed a Grade 1 pattern of invasion, tumor cells were detected from the subcapsular sinus to the follicles. After day 5, tumor-bearing LNs showed Grade CYTH4 2 or 3 invasion, the range of which extended to the paracortex in Grade 2 invasion. In Grade 3 invasion, >60% of LN-areas were occupied by tumors. In addition to tumor-invasion, these LNs showed expansion of the lymphatic medulla. A 2.8-, 4.4-, and 4.2-fold increase was observed in Grade 1, 2, and 3 LNs, respectively, when compared with untreated controls (Figure 3E). Changes in tumor-bearing SLNs were similar to those attributed to tumor-reactive lymphadenopathy in SLNs before metastasis. Figure 3 Tumor-bearing cervical lymph nodes in oral melanoma-bearing mice.