Exploring the significance of IgM expression in the lymphatic system during breast cancer progression

<h4>Background</h4>Breast cancer is a malignant tumor characterized by metastasis. It first spreads through the lymphatic system to lymph nodes of various levels and can subsequently metastasize to distant organs via the bloodstream. Therefore, identifying protein biomarkers associated with breast cancer is of great significance for predicting disease progression, implementing early drug therapy or interventions, and improving prognosis.This study aims to investigate the dynamic changes in immunoglobulin M (IgM) levels in lymphoid tissues and lymph fluid during the progression of breast cancer and to perform quantitative analysis using experimental methods.<h4>Methods</h4>Sixteen purebred female New Zealand White rabbits were selected from the Animal Experimentation Center of Ningxia Medical University to establish a breast cancer lymph node metastasis model. Lymph node implantation was performed on the experimental group, while a normal control group and a breast cancer control group were established. Lymph fluid was collected periodically from rabbits in each group, and breast tumor and sentinel lymph node (SLN) tissues were obtained at the end of the experiment. An enzyme-linked immunosorbent assay (ELISA) was used to analyze differences in IgM protein expression among different tissue groups, and immunohistochemical experiments were conducted to detect changes in Ki-67 expression. Proteomics techniques were employed to identify differentially expressed proteins in the lymphatic fluid of each group, and bioinformatics analysis was performed using the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases to screen for differentially expressed proteins and the relevant pathways in which they are involved.<h4>Results</h4>The expression of IgM proteins undergoes dynamic changes during the progression of breast cancer. ELISA results showed that IgM protein expression differed significantly among tissue groups (P≤0.05). Immunohistochemical analysis revealed significantly elevated Ki-67 expression in lymph node metastasis tissues (P≤0.05). Proteomic analysis identified a total of 270 differentially expressed proteins, including 4 significantly altered IgM-related proteins. These differentially expressed proteins are primarily involved in cellular metabolism and signaling pathways, such as the "NF-κB signaling pathway", "complement and coagulation cascade", and "B-cell receptor signaling pathway".<h4>Conclusions</h4>Through comparative analysis of lymphatic fluid and lymphoid tissue across different groups, this study identified multiple differentially expressed proteins in a rabbit model of breast cancer lymphatic metastasis. Currently, the specific associations of these proteins with breast cancer metastasis and proliferation remain unclear. The study suggests that IgM-related differentially expressed proteins warrant further attention, and their potential significance in breast cancer diagnosis awaits verification in subsequent studies.