Objective: Breast carcinoma in situ accounts for a significant number of newly diagnosed breast cancer cases. However, the cause of this type of cancer is unclear, which has led to debates regarding treatment strategies. A Mendelian randomization (MR) study was conducted to explore whether complement system or complement C1q/tumor necrosis factor-related proteins (CTRPs) are causally associated with breast carcinoma in situ.
Materials and methods: This two-sample multivariable MR study used genome-wide association study (GWAS) data for all complement system factors and CTRPs. Summary-level statistics were obtained from the breast carcinoma in situ GWAS database. The study employed the MR-Egger method, inverse variance weighted (IVW) method, and weighted median method. Additionally, sensitivity analyses, including the MR-Egger intercept, funnel plot, and leave-one-out analysis, were conducted to address uncertainties and enhance the reliability of the findings.
Results: The study indicated that certain immunomodulatory molecules might increase the risk of breast carcinoma in situ, with consistent results. Specifically, CTRP9 showed a 57.0% increased risk [IVW: odds ratio (OR) 0.570 (0.350, 0.928), p < 0.05], and complement factor H (FH)-related protein 5 (FHR-5) was linked to a 67.2% higher risk [IVW: OR 0.672 (0.477, 0.947), p < 0.05]. However, no associations were found with other molecules, suggesting the relationship between immunomodulatory molecules and cancer may be context-specific.
Conclusions: This MR study marks the initial identification of a direct link between FHR-5 and CTRP9 and the susceptibility to breast carcinoma in situ. Delving into the roles of immunomodulatory molecules and immune responses within the tumor microenvironment holds considerable importance for the management of breast carcinoma in situ.