Objective To evaluate the risk of recurrence or metastasis of breast cancer by LNG-IUS via meta-analysis. Methods We searched literature in the PubMed, Web of Science, Cochrane, EMBASE, CBM, CNKI, VIP, and WanFang database.The retrieval period was from January 2014 to October 2021.Data extraction and quality evaluation were conducted for the included randomized controlled study (RCT) to analyze whether LNG-IUS can increase the risk of recurrence or metastasis of breast cancer. Results A total of 1309 Chinese and English studies were retrieved; 5 RCTs were included in this study, and 446 patients were enrolled.The combined total effect value in the fixed-effect model with RD (95%CI)0.03(-0.03-0.08), Z=1.05, P=0.29) indicated that the LNG-IUS+tamoxifen group did not increase the risk of recurrence or metastasis of breast cancer compared with the tamoxifen group.The funnel diagram was basically symmetrical, suggesting that the publication bias was small. Conclusion Wearing the LNG-IUS does not increase the risk of relapse or metastasis of breast cancer significantly, and it provides certain safety for patients with breast cancer.

Cancer toxin is a specific pathogenesis leading to the heterogeneity of breast cancer.The nature and virulence of the cancer toxin determine the differences in the heterogeneity of breast cancer,which can dynamically evolve over time and space,resulting in varying invasion abilities and characteristics of the tumor.Cancer cells in the primary lesion possess"toxicity"that targets specific organs for metastasis,and cancer toxins can influence the metastatic propensity of different types of breast cancer.Therefore,breast cancer treatment strategies based on the theory of cancer toxins emphasize the continuous eradication of the cancer toxin,focusing on differentiating its strength and nature,protecting unaffected areas first,identifying the state based on symptoms,and targeting accordingly to combat resistance arising from tumor heterogeneity.This article aims to provide a new theoretical basis for the treatment strategies of different types of breast cancer.