Changes in the tumor microenvironment during lymphatic metastasis of lung squamous cell carcinoma

Abstract

Metastasis and growth in neoplastic lesions requires the multi-step regulation of microenvironmental factors. We aimed to elucidate the microenvironmental changes in the process of lymphatic metastasis of lung squamous cell carcinoma. We examined the morphological characteristics of 102 cases of Primary Tumor (PT), 50 of intralymphatic tumor (ILT), 51 of lymph node (LN) micrometastasis (LN-Mic; less than 2 mm in size) and 82 of LN macrometastasis (LN-Mac; greater than 10 mm in size). Afterwards we evaluated the expression of nine molecules (EGFR, FGFR2, CD44, ALDH1, Podoplanin, E-cadherin, S100A4, geminin and ezrin) in matched PT, ILT, LN-Mic and LN-Mac from 23 of these cases. The number of smooth muscle actin α-positive fibroblasts, CD34-positive microvessels and CD204-positive macrophages were also examined. As a result, the mitotic index of tumor cells was significantly lower in ILT and LN-Mic than PT and LN-Mac (p<0.001). Moreover stromal reaction in ILT and LN-Mic was less prominent than in PT and LN-Mac (p<0.001). Immunohistochemical study revealed that EGFR expression level and frequency of geminin positive cells in ILT and LN-Mic were significantly lower than in PT and LN-Mac (p<0.05). The number of stromal cells indicated by staining of CD34, CD204 and smooth muscle actin α in ILT and LN-Mic also was significantly lower than in PT and LN-Mac (p<0.05). In lung squamous cell carcinoma, drastic microenvironmental changes (e.g., growth factor receptor expression and proliferative capacity of tumor cells and structural changes in stromal cells) occur during both the process of lymphatic permeation and the progression into macrometastases.

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