Background: The modifications of connective tissue surrounding metastatic lymph nodes in a murine model of rectal cancer are described. Methods: Athymic nude mice (n = 36) were inoculated with 10 × 10 5 ht-29 cancer cells into the submucosal layer of the rectum. Control mice (n = 5) were treated with a sterile buffer. Tumor and the involved lymph nodes were visualized in vivo by magnetic resonance imaging at 1 to 4 weeks after cell injection. After the sacrifice, the excised samples were processed for histology. Results: After one week from cell injection all treated animals developed rectal cancer. Since the first week, neoplastic cells were visible in the nodes. In the surrounding connective tissue, the diameter of the adipocytes was reduced and a mesenchymal-like pattern with stellate cells embedded in an oedematous environment was visible. Since the second week, in the perinodal connective an enlargement of the stroma was present. The tissue was organized in cords and areas with extracellular accumulation of lipids were found. At the fourth week, we observed an enlargement of multilocular areas and lobules of elongated elements almost devoid of lipid droplets. In control animals, in absence of neoplastic masses, pelvic nodes were surrounded by a typical connective tissue characterized by unilocular adipocytes with groups of multilocular adipocytes. Conclusions: We have developed a model of rectal cancer with nodal metastases. Using this model, the work demonstrates that around secondary lesions, the morphogenetic events follow a standard evolution characterized by an early phase with lipolysis and mesenchymalization and later phases with a brown-like phenotype acquisition.
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