Abstract
Inflammatory biomarkers (including C-reactive protein [CRP], interleukin-6 [IL-6], procalcitonin [PCT], and serum amyloid A [SAA]) have been postulated to influence tumorigenesis, yet their causal relevance to breast cancer (BC) remains uncertain. We applied a two-sample Mendelian randomization (MR) framework to evaluate putative causal relationships between these circulating inflammatory factors and BC risk. Publicly available genome-wide association study summary statistics were used to identify, curate, and clump single-nucleotide polymorphisms that robustly trace CRP, IL-6, PCT, and SAA concentrations, which then served as instrumental variables. Causal estimates were generated with inverse-variance weighting, MR-Egger regression, weighted-median, simple-mode, and weighted-mode models. Heterogeneity was assessed by Cochran Q statistic, horizontal pleiotropy by the MR-Egger intercept, and robustness by leave-one-out as well as funnel-plot inspection. Two-sample MR demonstrated that genetically predicted SAA is positively associated with BC risk (inverse-variance weighting odds ratios = 1.002, 95% confidence interval 1.000–1.003, P = .023), whereas CRP, IL-6, and PCT exhibited no evidence of causal effects on BC in any MR model. Sensitivity analyses showed no substantial heterogeneity or directional pleiotropy, and causal estimates were stable after sequential SNP exclusion. In summary, the present MR study provides genetic evidence that elevated SAA causally increases the risk of developing BC, whereas CRP, IL-6, and PCT do not appear to exert independent causal influences.
Keywords: breast cancer, causal relationship, C-reactive protein, interleukin-6, Mendelian randomization, procalcitonin, serum amyloid A
1. Introduction
In recent years, the connection between inflammation and cancer has been a focal point of research, as inflammation is increasingly recognized as a critical factor in cancer development and progression. Inflammation contributes to various stages of cancer, including initiation, promotion, and metastasis. The tumor microenvironment, which includes inflammatory cells and cytokines, plays a significant role in supporting tumor growth and survival.[1–3] Chronic low-level inflammation is linked to the development and spread of many cancers. Breast cancer (BC) is one of the most common cancers in women, and its causes include genetics, environment, hormones, and the immune system.[4,5] In recent studies, inflammation factors like C-reactive protein (CRP), procalcitonin (PCT), interleukin-6 (IL-6), and serum amyloid A (SAA) have become important topics in cancer research. These factors are often used in clinical practice to check for inflammation in cancer patients and also show the development of tumors. Because of this, studying the link between these factors and BC is important for both science and treatment.
Mendelian randomization (MR) is a method that uses genetic differences to study cause and effect.[6,7] It has been used more in cancer and disease research. By looking at genetic differences linked to inflammation factors, MR can avoid problems in regular studies, like confusion or wrong conclusions.[8,9] In BC research, MR is a new way to find out if inflammation factors cause the disease. This study will look at how CRP, PCT, IL-6, and SAA affect the chance of getting BC using MR. We hope this study will help doctors better understand how to screen and prevent BC and find new ways to treat it.
2. Materials and methods
2.1. Research methods
This study used Mendelian randomization (MR) analysis to explore the causal relationship between inflammatory factors and BC, treating inflammatory factors (CRP, IL-6, PCT, and SAA) as exposures and BC as the outcome (Fig. 1). Sensitivity analyses were conducted to verify the reliability of MR results. MR analysis relies on 3 key assumptions (Fig. 2): ① relevance assumption: the instrumental SNPs must be strongly associated with the exposure; ② independence assumption: the instrumental variables must not be related to confounders affecting the outcome; ③ exclusion restriction assumption: the instrumental variables should affect the outcome only through the exposure.
Figure 1.
Flowchart of Mendelian randomization.
Figure 2.
Flowchart of 3 assumptions.
2.2. Data sources
All data used in this study were obtained from the IEU open genome-wide association study (GWAS) project database and are publicly available. CRP data from a 2022 GWAS (ebi-a-GCST90029070; n = 575,531; 10,713,245 SNPs). PCT data from a 2018 GWAS (prot-a-341; n = 3301; 10,534,735 SNPs). IL-6 data from a 2020 GWAS (ebi-a-GCST90012005; n = 21,758; 11,782,139 SNPs). SAA data from a 2020 GWAS (ebi-a-GCST90019411; n = 10,708; 15,567,814 SNPs). BC data from a 2018 GWAS (ukb-b-16890; n = 462,933; 10,303 cases and 452,630 controls; 9,851,867 SNPs). All samples were of European ancestry to minimize population stratification bias. Ethical approval was not required for using publicly available data (Table 1).
Table 1.
Genetic summary data sources for inflammatory factors and BC.
| Trait | Sample size | Population | ncase | ncontrol | Sex | PMID |
|---|---|---|---|---|---|---|
| CRP | 575,531 | European | NA | NA | Males and females | 35459240 |
| PCT | 3301 | European | NA | NA | Males and females | 29875488 |
| IL-6 | 21,758 | European | NA | NA | Males and females | 33067605 |
| SAA | 10,708 | European | NA | NA | Males and females | 33328453 |
| BC | 462,933 | European | 10,303 | 452,630 | Males and females | NA |
BC = breast cancer, CRP = C-reactive protein, IL-6 = interleukin-6, PCT = procalcitonin, SAA = serum amyloid A.
2.3. SNP selection
Using the R package TwoSampleMR, SNPs were selected based on MR assumptions. SNPs significantly associated with exposures (P < 5 × 10‐8) were filtered, with LD parameters set at r²=0.001 and kb = 10,000 to remove linked SNPs. Palindromic SNPs with intermediate allele frequencies were excluded. MR-PRESSO was used to identify and remove outlier SNPs. F-statistics (F > 10) were calculated to ensure instrument strength, using the formula F = β²/SE².
2.4. Statistical analysis
Data importation, SNP selection, MR analysis, and sensitivity analyses were performed using R software version 4.4.1 and the TwoSampleMR package (version 0.6.8).
2.4.1. MR analysis
The inverse-variance weighting (IVW) method was used as the primary analysis, supplemented by MR-Egger, weighted median, simple mode, and weighted mode methods. Odds ratios and 95% confidence intervals were calculated to assess the causal relationship. IVW is considered the most accurate MR method when there is no significant heterogeneity or horizontal pleiotropy (P > .05).
2.4.2. Sensitivity analysis
Several sensitivity analyses were conducted to validate the MR results. ① Horizontal pleiotropy was assessed using the MR-Egger intercept test (P > .05 indicates no pleiotropy). ② Heterogeneity was assessed using Cochran Q test for both IVW and MR-Egger methods (P > .05 indicates no heterogeneity). ③ Leave-one-out analysis assessed the influence of individual SNPs on the results. ④ Funnel plots were visually inspected for symmetry to detect bias.
3. Results
3.1. Instrumental variables
Two hundred sixty-four SNPs for CRP, 16 SNPs for PCT, 17 SNPs for IL-6, and 6 SNPs for SAA were included, all with F-statistics > 10, indicating no weak instrument bias (Tables 2–5).
Table 2.
A total of 264 independent SNPs strongly associated with the exposure were included for CRP.
| SNP | Effect | Other | chr | beta | se | pval | F |
|---|---|---|---|---|---|---|---|
| rs3935032 | T | C | 1 | ‐0.0153 | 0.0023 | 6.42E‐11 | 44.251 |
| rs12132412 | G | A | 1 | 0.0182 | 0.0021 | 1.70E‐17 | 75.111 |
| rs585406 | T | C | 1 | 0.0116 | 0.002 | 1.22E‐08 | 33.64 |
| rs469882 | C | A | 1 | ‐0.0349 | 0.0025 | 8.68E‐43 | 194.882 |
| rs2211320 | A | G | 1 | ‐0.1766 | 0.0021 | 1.00E‐200 | 7072.009 |
| rs630372 | A | G | 1 | 0.0154 | 0.0023 | 4.82E‐11 | 44.832 |
| rs10924372 | T | C | 1 | ‐0.0147 | 0.0021 | 6.18E‐12 | 49 |
| rs12239046 | C | T | 1 | 0.0404 | 0.002 | 1.34E‐87 | 408.04 |
| rs6695572 | A | G | 1 | 0.0143 | 0.0025 | 1.93E‐08 | 32.718 |
| rs78511209 | G | C | 1 | ‐0.0213 | 0.0035 | 7.60E‐10 | 37.036 |
| rs12730935 | A | G | 1 | ‐0.0936 | 0.002 | 1.00E‐200 | 2190.24 |
| rs55852476 | A | G | 1 | ‐0.0201 | 0.0031 | 4.68E‐11 | 42.041 |
| rs75460349 | C | A | 1 | ‐0.0948 | 0.0067 | 3.40E‐45 | 200.201 |
| rs3768321 | T | G | 1 | 0.0338 | 0.0025 | 3.06E‐40 | 182.79 |
| rs1353595 | C | A | 1 | 0.0282 | 0.0029 | 4.51E‐23 | 94.559 |
| rs197422 | A | C | 1 | 0.0123 | 0.002 | 1.54E‐09 | 37.822 |
| rs17417252 | G | A | 1 | 0.015 | 0.0022 | 2.13E‐11 | 46.488 |
| rs11118625 | G | A | 1 | ‐0.0194 | 0.0022 | 4.67E‐18 | 77.76 |
| rs11577023 | C | T | 1 | ‐0.0148 | 0.0021 | 4.45E‐12 | 49.669 |
| rs34298354 | T | C | 1 | ‐0.0278 | 0.0031 | 8.90E‐20 | 80.42 |
| rs301798 | G | A | 1 | 0.0117 | 0.0021 | 4.44E‐08 | 31.041 |
| rs34761529 | T | C | 1 | ‐0.0179 | 0.0025 | 2.03E‐12 | 51.266 |
| rs4655802 | A | G | 1 | ‐0.021 | 0.002 | 6.16E‐25 | 110.25 |
| rs2376015 | G | A | 1 | ‐0.118 | 0.002 | 1.00E‐200 | 3481 |
| rs797680 | T | G | 1 | ‐0.0144 | 0.002 | 1.53E‐12 | 51.84 |
| rs7528419 | G | A | 1 | 0.0159 | 0.0024 | 7.67E‐11 | 43.891 |
| rs34065906 | A | G | 1 | ‐0.0545 | 0.0027 | 1.79E‐87 | 407.442 |
| rs59519769 | G | A | 1 | ‐0.0355 | 0.0059 | 1.84E‐09 | 36.204 |
| rs2325924 | C | T | 1 | 0.0286 | 0.0022 | 2.46E‐37 | 169 |
| rs4433388 | G | C | 1 | 0.0501 | 0.002 | 1.15E‐133 | 627.502 |
| rs12025074 | G | A | 1 | 0.0181 | 0.0023 | 1.08E‐14 | 61.93 |
| rs10864088 | A | G | 1 | ‐0.016 | 0.0021 | 7.25E‐14 | 58.05 |
| rs12118890 | C | G | 1 | ‐0.0168 | 0.0029 | 3.79E‐09 | 33.56 |
| rs62104180 | A | G | 2 | ‐0.0315 | 0.0049 | 1.15E‐10 | 41.327 |
| rs13021775 | G | C | 2 | 0.0144 | 0.002 | 1.53E‐12 | 51.84 |
| rs13416992 | C | A | 2 | ‐0.0124 | 0.002 | 1.13E‐09 | 38.44 |
| rs12621948 | G | C | 2 | ‐0.0126 | 0.0022 | 1.85E‐08 | 32.802 |
| rs2970901 | T | G | 2 | 0.0134 | 0.002 | 4.68E‐11 | 44.89 |
| rs6734238 | G | A | 2 | 0.0449 | 0.002 | 9.53E‐108 | 504.003 |
| rs728455 | T | C | 2 | 0.0136 | 0.0021 | 2.01E‐10 | 41.941 |
| rs10497423 | T | G | 2 | ‐0.0134 | 0.002 | 4.68E‐11 | 44.89 |
| rs59916403 | T | G | 2 | 0.0166 | 0.0021 | 8.23E‐15 | 62.485 |
| rs13028310 | C | T | 2 | 0.026 | 0.0026 | 9.06E‐23 | 100 |
| rs11689543 | T | A | 2 | 0.0186 | 0.002 | 6.58E‐20 | 86.49 |
| rs35628191 | T | C | 2 | ‐0.012 | 0.002 | 3.79E‐09 | 36 |
| rs2161037 | A | G | 2 | 0.0205 | 0.002 | 7.70E‐24 | 105.063 |
| rs1869358 | C | T | 2 | ‐0.0169 | 0.0024 | 4.64E‐12 | 49.585 |
| rs10498240 | A | C | 2 | 0.0133 | 0.0021 | 4.95E‐10 | 40.111 |
| rs1260326 | C | T | 2 | ‐0.0758 | 0.002 | 1.00E‐200 | 1436.41 |
| rs2041748 | G | A | 2 | ‐0.0223 | 0.0023 | 1.68E‐21 | 94.006 |
| rs4849147 | T | A | 2 | 0.0169 | 0.0022 | 4.52E‐14 | 59.01 |
| rs77143791 | G | A | 2 | ‐0.033 | 0.0051 | 9.02E‐11 | 41.869 |
| rs6435156 | T | C | 2 | 0.0137 | 0.0023 | 4.90E‐09 | 35.48 |
| rs1441169 | G | A | 2 | ‐0.021 | 0.002 | 6.16E‐25 | 110.25 |
| rs12620844 | C | T | 2 | 0.0133 | 0.002 | 6.51E‐11 | 44.223 |
| rs7594775 | C | T | 2 | 0.0147 | 0.0021 | 6.18E‐12 | 49 |
| rs2054872 | A | C | 3 | 0.0175 | 0.0027 | 1.94E‐10 | 42.01 |
| rs6792725 | G | A | 3 | ‐0.0185 | 0.0022 | 1.46E‐16 | 70.713 |
| rs58936320 | A | T | 3 | 0.0123 | 0.0021 | 8.78E‐09 | 34.306 |
| rs13066686 | A | C | 3 | ‐0.0128 | 0.002 | 3.26E‐10 | 40.96 |
| rs11711864 | G | A | 3 | ‐0.0113 | 0.002 | 2.87E‐08 | 31.922 |
| rs3732356 | T | G | 3 | ‐0.0235 | 0.0042 | 1.81E‐08 | 31.307 |
| rs1969066 | A | G | 3 | 0.0133 | 0.0022 | 2.89E‐09 | 36.548 |
| rs1470560 | A | G | 3 | 0.0121 | 0.0021 | 1.52E‐08 | 33.2 |
| rs687339 | T | C | 3 | ‐0.0249 | 0.0024 | 2.19E‐24 | 107.641 |
| rs35415272 | AAAC | A | 3 | ‐0.0129 | 0.0023 | 3.61E‐08 | 31.457 |
| rs2596937 | C | T | 3 | 0.0173 | 0.0024 | 1.44E‐12 | 51.96 |
| rs6775319 | T | A | 3 | 0.0131 | 0.0022 | 4.96E‐09 | 35.457 |
| rs2280406 | A | G | 3 | 0.0222 | 0.002 | 1.12E‐27 | 123.21 |
| rs2310227 | T | G | 3 | ‐0.0119 | 0.0021 | 2.61E‐08 | 32.111 |
| rs6443429 | C | A | 3 | ‐0.0134 | 0.0021 | 3.67E‐10 | 40.717 |
| rs6801781 | G | A | 3 | ‐0.0129 | 0.0022 | 8.45E‐09 | 34.382 |
| rs1905505 | A | G | 3 | 0.0196 | 0.0022 | 2.13E‐18 | 79.372 |
| rs7662792 | T | A | 4 | 0.0166 | 0.0021 | 8.23E‐15 | 62.485 |
| rs10027275 | C | G | 4 | ‐0.0138 | 0.0023 | 3.79E‐09 | 36 |
| rs994596 | T | C | 4 | 0.0137 | 0.0021 | 1.48E‐10 | 42.56 |
| rs4832754 | C | T | 4 | ‐0.0126 | 0.0022 | 1.85E‐08 | 32.802 |
| rs45499402 | C | G | 4 | ‐0.019 | 0.0033 | 5.49E‐09 | 33.15 |
| rs201223023 | AC | A | 4 | 0.0134 | 0.0023 | 1.05E‐08 | 33.943 |
| rs141936164 | G | A | 4 | ‐0.0127 | 0.0021 | 2.85E‐09 | 36.574 |
| rs4690098 | T | C | 4 | 0.0167 | 0.0024 | 8.24E‐12 | 48.418 |
| rs166169 | C | T | 5 | 0.0188 | 0.0029 | 4.26E‐11 | 42.026 |
| rs142503704 | A | G | 5 | 0.0436 | 0.0079 | 4.02E‐08 | 30.459 |
| rs6595549 | C | G | 5 | ‐0.0155 | 0.0026 | 4.76E‐09 | 35.54 |
| rs6453434 | T | G | 5 | 0.0184 | 0.0021 | 7.58E‐18 | 76.771 |
| rs288183 | G | T | 5 | ‐0.0148 | 0.0026 | 2.26E‐08 | 32.402 |
| rs72799497 | C | T | 5 | 0.0166 | 0.0027 | 1.55E‐09 | 37.8 |
| rs2289852 | A | G | 5 | ‐0.0313 | 0.0044 | 8.72E‐13 | 50.604 |
| rs2608101 | C | T | 5 | 0.0143 | 0.0023 | 1.02E‐09 | 38.656 |
| rs11242113 | A | G | 5 | ‐0.0148 | 0.0025 | 6.08E‐09 | 35.046 |
| rs77704739 | C | T | 5 | ‐0.0483 | 0.0052 | 1.38E‐20 | 86.276 |
| rs750344 | A | G | 5 | 0.0158 | 0.0022 | 1.74E‐12 | 51.579 |
| rs3805433 | G | C | 5 | 0.0151 | 0.0022 | 1.57E‐11 | 47.11 |
| rs2161374 | T | C | 5 | ‐0.0191 | 0.002 | 6.60E‐21 | 91.202 |
| rs6925389 | G | A | 6 | 0.0149 | 0.0021 | 3.20E‐12 | 50.342 |
| rs13216424 | A | G | 6 | 0.0152 | 0.0026 | 9.35E‐09 | 34.178 |
| rs6905544 | G | A | 6 | 0.015 | 0.002 | 1.75E‐13 | 56.25 |
| rs654912 | C | T | 6 | ‐0.013 | 0.0022 | 6.48E‐09 | 34.917 |
| rs991946 | T | C | 6 | 0.0112 | 0.002 | 3.79E‐08 | 31.36 |
| rs4714508 | G | A | 6 | 0.0179 | 0.0021 | 5.67E‐17 | 72.655 |
| rs2307377 | G | A | 6 | 0.0221 | 0.0038 | 4.45E‐09 | 33.823 |
| rs174373 | C | T | 6 | ‐0.0135 | 0.0024 | 3.30E‐08 | 31.641 |
| rs4354188 | C | T | 6 | ‐0.018 | 0.002 | 9.60E‐19 | 81 |
| rs141783576 | C | G | 6 | ‐0.041 | 0.0046 | 3.59E‐19 | 79.442 |
| rs1338071 | C | G | 6 | 0.0163 | 0.0022 | 3.41E‐13 | 54.895 |
| rs5017416 | T | G | 6 | 0.0268 | 0.0047 | 1.05E‐08 | 32.514 |
| rs1490384 | T | C | 6 | ‐0.0279 | 0.002 | 9.94E‐43 | 194.603 |
| rs12202212 | T | C | 6 | 0.0119 | 0.0021 | 2.61E‐08 | 32.111 |
| rs6920220 | A | G | 6 | 0.0219 | 0.0024 | 3.17E‐19 | 83.266 |
| rs3808348 | T | C | 7 | ‐0.0224 | 0.0025 | 1.36E‐18 | 80.282 |
| rs1880241 | G | A | 7 | -0.0252 | 0.002 | 3.54E‐35 | 158.76 |
| rs12673996 | T | C | 7 | ‐0.027 | 0.0024 | 2.20E‐28 | 126.563 |
| rs62451586 | A | G | 7 | ‐0.02 | 0.0033 | 8.32E‐10 | 36.731 |
| rs1918912 | T | C | 7 | ‐0.0124 | 0.0022 | 3.10E‐08 | 31.769 |
| rs35462231 | T | A | 7 | ‐0.0212 | 0.0024 | 4.10E‐18 | 78.028 |
| rs73476799 | G | A | 7 | 0.0414 | 0.0071 | 6.29E‐09 | 34 |
| rs7794705 | G | A | 7 | ‐0.0259 | 0.0027 | 4.44E‐21 | 92.018 |
| rs114947103 | C | T | 7 | 0.0157 | 0.0026 | 3.01E‐09 | 36.463 |
| rs17196595 | T | C | 7 | ‐0.0141 | 0.0023 | 1.73E‐09 | 37.582 |
| rs79941637 | T | A | 7 | ‐0.0292 | 0.0045 | 7.12E‐11 | 42.106 |
| rs2700938 | C | T | 7 | 0.0236 | 0.0021 | 2.51E‐28 | 126.295 |
| rs73137144 | G | A | 7 | ‐0.0186 | 0.0026 | 2.12E‐12 | 51.178 |
| rs35695283 | G | A | 7 | ‐0.0372 | 0.0031 | 4.02E‐34 | 144 |
| rs113184201 | A | G | 7 | 0.0144 | 0.0021 | 1.64E‐11 | 47.02 |
| rs7801838 | T | C | 7 | ‐0.0128 | 0.0022 | 1.10E‐08 | 33.851 |
| rs7012637 | A | G | 8 | 0.0499 | 0.002 | 1.29E‐132 | 622.502 |
| rs6992315 | T | C | 8 | ‐0.0135 | 0.0022 | 1.67E‐09 | 37.655 |
| rs11786900 | C | G | 8 | ‐0.0368 | 0.0035 | 2.14E‐26 | 110.55 |
| rs685218 | A | C | 8 | 0.0137 | 0.0021 | 1.48E‐10 | 42.56 |
| rs11782130 | T | G | 8 | 0.0123 | 0.0021 | 8.78E‐09 | 34.306 |
| rs10106298 | A | G | 8 | 0.0151 | 0.0021 | 1.64E‐12 | 51.703 |
| rs1545536 | T | C | 8 | ‐0.0244 | 0.0025 | 9.14E‐22 | 95.258 |
| rs10095930 | T | C | 8 | 0.0286 | 0.002 | 8.23E‐45 | 204.49 |
| rs13261587 | T | C | 8 | 0.0204 | 0.002 | 1.27E‐23 | 104.04 |
| rs112875651 | A | G | 8 | ‐0.0202 | 0.0021 | 3.46E‐21 | 92.526 |
| rs424539 | G | C | 9 | 0.012 | 0.0021 | 1.99E‐08 | 32.653 |
| rs1935237 | C | A | 9 | 0.0198 | 0.0027 | 5.90E‐13 | 53.778 |
| rs78428995 | C | T | 9 | 0.0203 | 0.002 | 2.08E‐23 | 103.022 |
| rs10760691 | G | A | 9 | 0.0172 | 0.0021 | 8.65E‐16 | 67.084 |
| rs13294945 | G | T | 9 | ‐0.0137 | 0.0024 | 2.06E‐08 | 32.585 |
| rs10868852 | A | C | 9 | 0.0344 | 0.006 | 1.02E‐08 | 32.871 |
| rs505922 | C | T | 9 | 0.0239 | 0.0021 | 5.21E‐29 | 129.526 |
| rs10969334 | A | C | 9 | ‐0.0112 | 0.002 | 3.79E‐08 | 31.36 |
| rs10797119 | C | T | 9 | 0.0177 | 0.002 | 3.55E‐18 | 78.322 |
| rs12251016 | T | A | 10 | 0.0144 | 0.0021 | 1.64E‐11 | 47.02 |
| rs7908825 | G | C | 10 | 0.0133 | 0.002 | 6.51E‐11 | 44.223 |
| rs303429 | T | C | 10 | ‐0.0152 | 0.002 | 8.35E‐14 | 57.76 |
| rs1332328 | T | C | 10 | 0.0265 | 0.0021 | 2.81E‐35 | 159.24 |
| rs7084062 | G | A | 10 | 0.0133 | 0.0021 | 4.95E‐10 | 40.111 |
| rs704017 | G | A | 10 | ‐0.016 | 0.002 | 3.92E‐15 | 64 |
| rs835278 | T | A | 10 | ‐0.015 | 0.0021 | 2.29E‐12 | 51.02 |
| rs10831676 | C | A | 11 | ‐0.0118 | 0.002 | 6.84E‐09 | 34.81 |
| rs1222209 | A | C | 11 | ‐0.0146 | 0.0021 | 8.58E‐12 | 48.336 |
| rs2956395 | G | C | 11 | 0.0145 | 0.0021 | 1.19E‐11 | 47.676 |
| rs1401454 | T | C | 11 | ‐0.0129 | 0.002 | 2.37E‐10 | 41.602 |
| rs4755726 | G | T | 11 | ‐0.0167 | 0.0022 | 8.94E‐14 | 57.622 |
| rs7127808 | T | A | 11 | 0.0206 | 0.0026 | 7.14E‐15 | 62.775 |
| rs663015 | C | T | 11 | 0.0167 | 0.0021 | 5.69E‐15 | 63.24 |
| rs34092660 | C | T | 11 | ‐0.0128 | 0.0022 | 1.10E‐08 | 33.851 |
| rs62618693 | T | C | 11 | ‐0.0296 | 0.0051 | 6.08E‐09 | 33.686 |
| rs6486122 | T | C | 11 | 0.0296 | 0.0021 | 1.38E‐43 | 198.676 |
| rs7103411 | T | C | 11 | 0.0216 | 0.0024 | 9.60E‐19 | 81 |
| rs4647725 | C | T | 11 | ‐0.0333 | 0.0027 | 8.94E‐34 | 152.111 |
| rs7933202 | C | A | 11 | ‐0.021 | 0.002 | 6.16E‐25 | 110.25 |
| rs11047224 | C | G | 12 | ‐0.0522 | 0.0054 | 3.90E‐22 | 93.444 |
| rs1800973 | A | C | 12 | 0.0294 | 0.0043 | 6.18E‐12 | 46.747 |
| rs7970695 | A | G | 12 | 0.1496 | 0.002 | 1.00E‐200 | 5595.04 |
| rs117316622 | T | C | 12 | 0.042 | 0.0076 | 3.79E‐08 | 30.54 |
| rs1800693 | C | T | 12 | ‐0.0218 | 0.002 | 9.56E‐27 | 118.81 |
| rs4963725 | T | C | 12 | 0.0163 | 0.003 | 3.38E‐08 | 29.521 |
| rs2465585 | G | A | 12 | ‐0.0224 | 0.0025 | 1.36E‐18 | 80.282 |
| rs77738620 | T | C | 12 | ‐0.0588 | 0.0099 | 2.62E‐09 | 35.276 |
| rs4764939 | T | C | 12 | ‐0.0201 | 0.002 | 5.56E‐23 | 101.003 |
| rs112303588 | C | G | 12 | 0.045 | 0.0063 | 1.01E‐12 | 51.02 |
| rs2668244 | G | C | 12 | 0.0286 | 0.0038 | 3.15E‐14 | 56.645 |
| rs9738365 | A | C | 12 | 0.0212 | 0.0023 | 1.39E‐19 | 84.96 |
| rs6582586 | A | G | 12 | 0.0114 | 0.002 | 2.16E‐08 | 32.49 |
| rs17098829 | C | G | 12 | ‐0.0129 | 0.0023 | 3.61E‐08 | 31.457 |
| rs4842708 | T | C | 12 | ‐0.0149 | 0.002 | 2.53E‐13 | 55.503 |
| rs2126886 | T | C | 12 | ‐0.0172 | 0.0024 | 1.94E‐12 | 51.361 |
| rs2657896 | T | C | 12 | ‐0.0233 | 0.0027 | 2.33E‐17 | 74.471 |
| rs2393794 | C | T | 12 | 0.0367 | 0.0026 | 1.05E‐43 | 199.244 |
| rs72656645 | G | A | 12 | 0.015 | 0.0022 | 2.13E‐11 | 46.488 |
| rs7302913 | A | G | 12 | ‐0.0279 | 0.002 | 9.94E‐43 | 194.603 |
| rs12229097 | T | C | 12 | ‐0.0133 | 0.0023 | 1.35E‐08 | 33.439 |
| rs17691879 | T | C | 13 | ‐0.015 | 0.0027 | 4.85E‐08 | 30.864 |
| rs11617494 | A | G | 13 | 0.0144 | 0.0024 | 3.79E‐09 | 36 |
| rs7993752 | A | C | 13 | ‐0.0134 | 0.002 | 4.68E‐11 | 44.89 |
| rs9604045 | T | G | 13 | ‐0.0229 | 0.0027 | 8.06E‐17 | 71.936 |
| rs2786178 | C | T | 13 | ‐0.0142 | 0.0025 | 2.42E‐08 | 32.262 |
| rs11159021 | C | T | 14 | 0.0118 | 0.0021 | 3.41E‐08 | 31.574 |
| rs6573778 | C | T | 14 | 0.0179 | 0.002 | 1.49E‐18 | 80.102 |
| rs146424514 | A | G | 14 | 0.0159 | 0.0027 | 7.30E‐09 | 34.679 |
| rs55772175 | C | T | 14 | ‐0.0171 | 0.0021 | 1.27E‐15 | 66.306 |
| rs17781691 | G | A | 14 | ‐0.0188 | 0.002 | 2.64E‐20 | 88.36 |
| rs76014628 | T | C | 14 | ‐0.0142 | 0.0024 | 6.20E‐09 | 35.007 |
| rs56047269 | T | C | 14 | 0.014 | 0.0022 | 4.10E‐10 | 40.496 |
| rs28929474 | T | C | 14 | ‐0.1003 | 0.0074 | 1.67E‐41 | 183.712 |
| rs34864350 | G | A | 14 | 0.0301 | 0.0046 | 5.04E‐11 | 42.817 |
| rs2239222 | G | A | 14 | 0.0359 | 0.0021 | 2.85E‐63 | 292.247 |
| rs4776150 | A | G | 15 | ‐0.0182 | 0.002 | 3.97E‐19 | 82.81 |
| rs340005 | A | G | 15 | 0.0339 | 0.0021 | 1.29E‐56 | 260.592 |
| rs9788721 | T | C | 15 | ‐0.0121 | 0.0021 | 1.52E‐08 | 33.2 |
| rs55707100 | T | C | 15 | 0.0692 | 0.0063 | 5.79E‐28 | 120.651 |
| rs60669734 | T | C | 15 | ‐0.0287 | 0.0034 | 1.32E‐17 | 71.253 |
| rs56187480 | A | G | 15 | ‐0.0156 | 0.0021 | 2.96E‐13 | 55.184 |
| rs728538 | G | T | 16 | 0.0397 | 0.0027 | 2.82E‐47 | 216.199 |
| rs4988483 | A | C | 16 | 0.0278 | 0.0051 | 4.74E‐08 | 29.713 |
| rs2726033 | G | A | 16 | 0.0151 | 0.0022 | 1.57E‐11 | 47.11 |
| rs28429148 | A | G | 16 | 0.0247 | 0.0021 | 7.18E‐31 | 138.342 |
| rs12933677 | C | T | 16 | 0.0137 | 0.002 | 1.72E‐11 | 46.923 |
| rs60037105 | A | T | 16 | 0.0183 | 0.0022 | 3.08E‐16 | 69.192 |
| rs6500446 | G | A | 16 | ‐0.0114 | 0.002 | 2.16E‐08 | 32.49 |
| rs12716972 | G | A | 16 | 0.0115 | 0.002 | 1.63E‐08 | 33.062 |
| rs141179989 | T | C | 16 | ‐0.0572 | 0.0097 | 3.34E‐09 | 34.774 |
| rs66985888 | G | A | 16 | ‐0.035 | 0.0059 | 3.08E‐09 | 35.191 |
| rs4018180 | A | G | 16 | ‐0.0317 | 0.0042 | 3.10E‐14 | 56.967 |
| rs17616063 | G | A | 16 | ‐0.1338 | 0.0044 | 1.00E‐200 | 924.713 |
| rs12929503 | C | T | 16 | ‐0.0161 | 0.002 | 2.64E‐15 | 64.803 |
| rs12927172 | G | A | 16 | ‐0.0193 | 0.002 | 2.59E‐21 | 93.123 |
| rs62089592 | A | G | 17 | 0.0142 | 0.0021 | 3.11E‐11 | 45.723 |
| rs992072 | T | G | 17 | ‐0.0148 | 0.0022 | 3.91E‐11 | 45.256 |
| rs7217663 | T | C | 17 | ‐0.0213 | 0.0035 | 7.60E‐10 | 37.036 |
| rs1557812 | A | G | 17 | 0.0153 | 0.0024 | 3.81E‐10 | 40.641 |
| rs8070176 | T | C | 17 | ‐0.015 | 0.0023 | 1.50E‐10 | 42.533 |
| rs11658216 | T | C | 17 | 0.0274 | 0.0024 | 3.51E‐29 | 130.34 |
| rs178826 | T | C | 17 | 0.0158 | 0.002 | 8.54E‐15 | 62.41 |
| rs17138478 | A | C | 17 | 0.0338 | 0.0032 | 9.23E‐27 | 111.566 |
| rs8072566 | A | G | 17 | ‐0.0204 | 0.0025 | 1.11E‐15 | 66.586 |
| rs1292061 | G | A | 17 | 0.0209 | 0.002 | 1.02E‐24 | 109.202 |
| rs11078597 | C | T | 17 | ‐0.0187 | 0.0026 | 1.62E‐12 | 51.729 |
| rs149394327 | C | G | 17 | 0.0593 | 0.0063 | 5.77E‐21 | 88.599 |
| rs1037170 | T | C | 17 | 0.0281 | 0.0023 | 3.56E‐33 | 149.265 |
| rs11868378 | A | G | 17 | ‐0.0334 | 0.0027 | 5.73E‐34 | 153.026 |
| rs2542153 | C | T | 18 | 0.0237 | 0.002 | 2.61E‐31 | 140.422 |
| rs9965184 | T | A | 18 | ‐0.0118 | 0.0021 | 3.41E‐08 | 31.574 |
| rs2339102 | T | C | 18 | 0.0125 | 0.002 | 8.32E‐10 | 39.063 |
| rs55855238 | C | T | 18 | 0.027 | 0.0021 | 1.48E‐36 | 165.306 |
| rs12605964 | T | C | 18 | 0.0141 | 0.0021 | 4.26E‐11 | 45.082 |
| rs10871777 | G | A | 18 | 0.0196 | 0.0023 | 5.76E‐17 | 72.62 |
| rs34866669 | C | G | 18 | 0.0137 | 0.0021 | 1.48E‐10 | 42.56 |
| rs123698 | C | G | 19 | ‐0.0132 | 0.0022 | 3.79E‐09 | 36 |
| rs62119267 | C | A | 19 | 0.0505 | 0.0071 | 1.38E‐12 | 50.59 |
| rs429358 | C | T | 19 | ‐0.2652 | 0.0029 | 1.00E‐200 | 8362.787 |
| rs59737437 | T | C | 19 | -0.015 | 0.0023 | 1.50E‐10 | 42.533 |
| rs58542926 | T | C | 19 | 0.0356 | 0.0039 | 3.53E‐20 | 83.324 |
| rs199956232 | CT | C | 19 | ‐0.0673 | 0.0027 | 2.30E‐132 | 621.302 |
| rs10420434 | A | G | 19 | 0.0598 | 0.005 | 4.17E‐33 | 143.042 |
| rs117627359 | T | C | 19 | ‐0.0343 | 0.0056 | 9.05E‐10 | 37.516 |
| rs373043655 | T | C | 19 | ‐0.05 | 0.0072 | 4.62E‐12 | 48.225 |
| rs117664574 | G | C | 19 | 0.087 | 0.0069 | 3.24E‐36 | 158.979 |
| rs2207132 | A | G | 20 | 0.0487 | 0.006 | 5.18E‐16 | 65.88 |
| rs1800961 | T | C | 20 | ‐0.1074 | 0.0059 | 6.50E‐74 | 331.363 |
| rs74616372 | C | T | 20 | ‐0.0228 | 0.0036 | 1.57E‐10 | 40.111 |
| rs6070563 | G | A | 20 | 0.0129 | 0.0021 | 1.60E‐09 | 37.735 |
| rs6090040 | C | A | 20 | ‐0.0154 | 0.002 | 3.94E‐14 | 59.29 |
| rs2260997 | T | G | 20 | 0.0178 | 0.002 | 2.30E‐18 | 79.21 |
| rs1056441 | C | T | 20 | 0.0208 | 0.0021 | 2.28E‐22 | 98.104 |
| rs9977825 | C | T | 21 | ‐0.0122 | 0.0021 | 1.16E‐08 | 33.751 |
| rs16988471 | C | A | 21 | 0.0336 | 0.0049 | 6.18E‐12 | 47.02 |
| rs4817984 | A | C | 21 | ‐0.0344 | 0.0022 | 3.14E‐53 | 244.496 |
| rs6519133 | C | T | 22 | ‐0.0313 | 0.0021 | 1.58E‐48 | 222.152 |
| rs4821764 | A | G | 22 | ‐0.0132 | 0.002 | 9.02E‐11 | 43.56 |
| rs111298861 | T | G | 22 | ‐0.0159 | 0.002 | 5.79E‐15 | 63.203 |
CRP = C-reactive protein.
Table 5.
A total of 6 independent SNPs strongly associated with the exposure were included for SAA.
| SNP | Effect | Other | chr | beta | se | pval | F |
|---|---|---|---|---|---|---|---|
| rs1938498 | C | T | 1 | ‐0.1633 | 0.0136 | 5.26E‐33 | 144.177 |
| rs2668202 | G | A | 3 | ‐0.1232 | 0.0138 | 5.45E‐19 | 79.701 |
| rs746463 | T | C | 11 | ‐0.0884 | 0.0145 | 1.14E‐09 | 37.168 |
| rs12286251 | G | A | 11 | 0.1345 | 0.0179 | 6.00E‐14 | 56.46 |
| rs11606304 | G | T | 11 | 0.1807 | 0.0255 | 1.24E‐12 | 50.215 |
| rs11024589 | C | A | 11 | ‐0.6126 | 0.0224 | 2.17E‐164 | 747.925 |
SAA = serum amyloid A, SNPs = single nucleotide polymorphisms.
Table 3.
A total of 16 independent SNPs strongly associated with the exposure were included for PCT.
| SNP | Effect | Other | chr | beta | se | pval | F |
|---|---|---|---|---|---|---|---|
| rs12043613 | G | A | 1 | 0.2118 | 0.0449 | 2.34E‐06 | 22.251 |
| rs141164217 | C | A | 2 | 0.6489 | 0.1411 | 4.27E‐06 | 21.15 |
| rs2270263 | T | C | 2 | 0.1351 | 0.0264 | 3.16E‐07 | 26.188 |
| rs145214525 | A | G | 2 | ‐0.5883 | 0.1208 | 1.12E‐06 | 23.717 |
| rs76051678 | A | G | 6 | ‐0.2321 | 0.0503 | 3.98E‐06 | 21.292 |
| rs9474592 | C | A | 6 | ‐0.1542 | 0.0309 | 6.31E‐07 | 24.903 |
| rs147828190 | T | C | 7 | 0.4433 | 0.0807 | 3.98E‐08 | 30.175 |
| rs13288876 | A | G | 9 | ‐0.2279 | 0.049 | 3.31E‐06 | 21.632 |
| rs114802537 | A | G | 10 | 0.5487 | 0.1166 | 2.51E‐06 | 22.145 |
| rs57626295 | G | T | 11 | ‐0.1324 | 0.0282 | 2.75E‐06 | 22.043 |
| rs78816719 | C | T | 12 | 0.3072 | 0.0671 | 4.68E‐06 | 20.96 |
| rs1446528 | G | A | 12 | 0.1375 | 0.028 | 9.12E‐07 | 24.115 |
| rs113712971 | T | C | 13 | ‐0.233 | 0.0507 | 4.27E‐06 | 21.12 |
| rs74093831 | A | C | 14 | 0.1487 | 0.028 | 1.15E‐07 | 28.204 |
| rs61986621 | T | C | 14 | 0.145 | 0.0314 | 3.80E‐06 | 21.324 |
| rs2427459 | T | C | 20 | 0.1166 | 0.025 | 3.16E‐06 | 21.753 |
PCT = procalcitonin.
Table 4.
A total of 17 independent SNPs strongly associated with the exposure were included for IL-6.
| SNP | Effect | Other | chr | beta | se | pval. | F |
|---|---|---|---|---|---|---|---|
| rs111572787 | T | C | 1 | 0.4099 | 0.0893 | 4.44E‐06 | 21.069 |
| rs2228145 | C | A | 1 | 0.1747 | 0.0124 | 3.34E‐45 | 198.492 |
| rs192869620 | A | G | 1 | ‐0.4749 | 0.0954 | 6.44E‐07 | 24.78 |
| rs148924545 | G | A | 1 | ‐0.1821 | 0.0379 | 1.51E‐06 | 23.086 |
| rs1444691 | G | A | 2 | ‐0.0573 | 0.0122 | 2.69E‐06 | 22.059 |
| rs9811834 | T | A | 3 | ‐0.0679 | 0.0147 | 4.11E‐06 | 21.336 |
| rs80316479 | T | C | 3 | ‐0.1956 | 0.0418 | 2.92E‐06 | 21.897 |
| rs34032964 | T | A | 4 | ‐0.4095 | 0.0884 | 3.57E‐06 | 21.459 |
| rs7448500 | G | C | 5 | 0.0631 | 0.0128 | 8.68E‐07 | 24.302 |
| rs4959106 | C | T | 6 | 0.0823 | 0.0138 | 2.37E‐09 | 35.567 |
| rs76598619 | C | T | 7 | ‐0.2511 | 0.0506 | 7.01E‐07 | 24.626 |
| rs35119607 | T | C | 11 | 0.1295 | 0.0284 | 4.99E‐06 | 20.792 |
| rs144530765 | G | A | 11 | ‐0.3623 | 0.0731 | 7.16E‐07 | 24.564 |
| rs1530088 | T | C | 16 | 0.068 | 0.0147 | 3.95E‐06 | 21.398 |
| rs2288477 | G | A | 19 | ‐0.0617 | 0.0133 | 3.74E‐06 | 21.521 |
| rs4802241 | C | A | 19 | ‐0.0791 | 0.0166 | 1.85E‐06 | 22.706 |
| rs2651097 | A | G | 19 | ‐0.071 | 0.0155 | 4.52E‐06 | 20.982 |
IL-6 = interleukin-6.
3.1.1. MR analysis results
IVW, MR-Egger, weighted median, simple mode, and weighted mode analyses consistently indicated no causal relationship between CRP, IL-6, PCT, and BC (P > .05). IVW analysis suggested that SAA increases BC risk [odds ratios = 1.002, 95% confidence interval (1.000, 1.003), P = .023]. Although other methods did not show a significant association for SAA, IVW as the primary method supports a causal relationship (P < .05) (Table 6).
Table 6.
The causal effect of different inflammatory factors and BC.
| Exposure | Outcome | IVW | MR-Egger | Weighted median | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| OR (95 % CI) |
P | Q | P | OR (95 % CI) |
P | Q | P | OR (95 % CI) |
P | ||
| CRP | BC | 1.000 (0.998–1.002) | .992 | 327.881 | .000 | 1.000 (0.998–1.002) | .799 | 327.372 | .000 | 1.000 (0.998–1.002) | .996 |
| PCT | BC | 1.000 (0.998–1.001) | .741 | 13.014 | .223 | 0.996 (0.988–1.004) | .363 | 11.919 | .218 | 1.000 (0.996–1.003) | .568 |
| IL-6 | BC | 1.000 (0.998–1.003) | .836 | 1.954 | .992 | 1.002 (0.996–1.007) | .537 | 1.576 | .991 | 1.001 (0.997–1.004) | .741 |
| SAA | BC | 1.002 (1.000–1.003) | .023 | 2.106 | .716 | 1.001 (0.999–1.003) | .429 | 1.652 | .648 | 1.001 (0.999–1.003) | .164 |
BC = breast cancer, CI = confidence interval, CRP = C-reactive protein, IL-6 = interleukin-6, IVW = inverse-variance weighting, OR = odds ratios, P = P value, PCT = procalcitonin, Q = cochran Q, SAA = serum amyloid A.
3.2. Sensitivity analyses
Heterogeneity tests for PCT, IL-6, and SAA showed no heterogeneity (IVW: Q = 13.014, P = .223; Q = 1.954, P = .992; Q = 2.106, P = .716). MR-Egger heterogeneity tests also showed no heterogeneity. MR-Egger intercept tests showed no evidence of horizontal pleiotropy for PCT, IL-6, or SAA (Table 7). Leave-one-out analyses indicated that no single SNP influenced the causal estimates significantly (Figs. 3–5). Funnel plots were largely symmetrical, suggesting minimal bias (Figs. 6–8).
Table 7.
Horizontal pleiotropy in different inflammatory factors and BC.
| Exposure | Outcome | Egger_intercept | P value |
|---|---|---|---|
| CRP | BC | ‐0.000 | .717 |
| PCT | BC | 0.001 | .387 |
| IL-6 | BC | ‐0.000 | .556 |
| SAA | BC | 0.000 | .549 |
BC = breast cancer, CRP = C-reactive protein, IL-6 = interleukin-6, PCT = procalcitonin, SAA = serum amyloid A.
Figure 3.
The leave-one-out method for the causal effect of PCT on breast cancer. PCT = procalcitonin.
Figure 5.
The leave-one-out method for the causal effect of SAA on breast cancer. SAA = serum amyloid A.
Figure 6.
Funnel plot of the causal effect of PCT on breast cancer. PCT = procalcitonin.
Figure 8.
Funnel plot of the causal effect of SAA on breast cancer. SAA = serum amyloid A.
Figure 4.
The leave-one-out method for the causal effect of IL-6 on breast cancer. IL-6 = interleukin-6.
Figure 7.
Funnel plot of the causal effect of IL-6 on breast cancer. IL-6 = interleukin-6.
For CRP, heterogeneity was detected (IVW: Q = 327.881, P < .01; MR-Egger: Q = 327.372, P < .01) but did not affect the overall conclusion. No evidence of horizontal pleiotropy was found (Egger intercept = ‐0.000, P = .717). Leave-one-out analysis confirmed that no single SNP significantly influenced the causal inference (Fig. 9). Funnel plots were largely symmetrical, indicating minimal bias (Fig. 10).
Figure 9.
The leave-one-out method for the causal effect of CRP on breast cancer. CRP = C-reactive protein.
Figure 10.
Funnel plot of the causal effect of CRP on breast cancer. CRP = C-reactive protein.
4. Discussion
This study used two-sample Mendelian randomization to explore the causal relationship between inflammatory factors and BC. Inflammatory factors are widely considered to play an important role in the occurrence and development of various cancers, particularly in the immune microenvironment of BC, where they may promote tumor development by regulating tumor cell proliferation, metastasis, and immune evasion. However, traditional observational studies often suffer from confounding factors and biases, making it difficult to draw clear causal conclusions. To overcome these limitations, this study used genetic instrumental variables, effectively eliminating these potential biases, and providing more reliable causal inference. The results of the study suggest a significant causal relationship between SAA and BC, while no such relationship was found for PCT, CRP, and IL-6, offering new insights into the different roles of inflammatory factors in the development of BC.
CRP is a widely used inflammatory marker. Its levels typically rise in response to systemic inflammation. Many studies suggest that CRP is associated with the occurrence, metastasis, and prognosis of BC.[10,11] Elevated CRP usually reflects a chronic inflammatory response, and such inflammation may influence tumor growth and metastasis.[12] Therefore, CRP is often considered a potential risk factor for BC, particularly in the prognosis assessment of BC patients.
However, in this study, Mendelian randomization analysis did not find a causal relationship between CRP and BC. While many observational studies found that elevated CRP levels are associated with increased BC risk, these studies cannot completely rule out other influencing factors.[13,14] By using Mendelian randomization, we were able to control for these confounding factors and concluded that there is no direct causal relationship between CRP and BC. The elevation of CRP may be caused by other health issues, such as obesity or diabetes, which themselves may be associated with increased BC risk. Overall, elevated CRP reflects a chronic inflammatory state in the body rather than being an independent risk factor for BC.
Interleukin-6 (IL-6) is a pro-inflammatory cytokine that plays an important role in the occurrence and progression of many cancers.[15] IL-6 activates specific signaling pathways, promoting the proliferation, metastasis, and immune evasion of tumor cells.[16] In BC, IL-6 is considered a factor associated with tumor malignancy and metastasis.[17] Many studies have shown that IL-6 may play a role in promoting the development of BC.[18,19]
However, Mendelian randomization analysis in this study did not find a clear causal relationship between IL-6 and BC. IL-6 is influenced not only by BC itself but also by other factors, such as systemic inflammation and metabolic issues.[20] Therefore, the elevation of IL-6 may not be directly caused by the occurrence of BC but by inflammation resulting from other health problems. Although IL-6 may play an important role in the immune microenvironment of BC, it is not the direct cause of BC.
SAA is a significant acute-phase protein that has been implicated in the pathogenesis of various cancers, including BC. Its role in inflammation and cancer progression is well-documented, highlighting its potential as a biomarker for cancer diagnosis and prognosis. In BC, SAA levels have been shown to correlate with disease progression and recurrence, making it a valuable marker for monitoring patient outcomes and treatment efficacy.[21] The diagnostic importance of SAA in BC is further supported by studies that have demonstrated its elevated levels in patients compared to healthy controls. These findings suggest that SAA, along with other markers, could be used to improve the accuracy of BC diagnosis and to differentiate between cancerous and noncancerous conditions.[21–23] Moreover, the expression patterns of acute-phase proteins, including SAA, have been associated with BC, colorectal cancer, and lung cancer.[24] These proteins exhibit distinctive expression profiles that can be utilized to develop biomarker panels for early detection and monitoring of cancer progression.[25]
In this study, Mendelian randomization found a significant causal relationship between SAA and BC. The results suggest that elevated SAA levels may increase the risk of developing BC. SAA is not just a marker of inflammation; it may also regulate the immune system, influence the tumor microenvironment, and promote tumor growth and metastasis. Compared to other inflammatory factors, SAA may have a more direct role in BC, making its elevation an important biological marker of BC development.
5. Limitation
Although this study used Mendelian randomization to explore the causal relationship between inflammatory factors and BC and drew some important conclusions, there are still certain limitations. First, the study relied on existing GWAS data, and the choice of instrumental variables may affect the accuracy of the results. Future research could use larger genetic datasets to further validate the causal relationships between these inflammatory factors and BC. Second, the study included only populations of European descent, and future studies could consider including other diverse populations.
6. Conclusion
In this study, we used two-sample Mendelian randomization to investigate the causal relationship between inflammatory factors and BC. The results showed a clear causal relationship between SAA and BC, suggesting that SAA may increase the risk of BC by affecting inflammation and the immune environment. In contrast, no direct causal relationship was found between PCT, CRP, and IL-6 and BC, meaning they may not be major factors in the development of BC. However, these inflammatory factors may still play a role in immune evasion and prognosis assessment in BC. Future research needs to further confirm these findings, especially in different populations and BC subtypes, to provide more accurate theoretical support for early diagnosis, prevention, and personalized treatment of BC.
Author contributions
Conceptualization: Qiang Hu.
Data curation: Qiang Hu.
Formal analysis: Qiang Hu.
Funding acquisition: Qiang Hu.
Methodology: Xiyin Yang, Qiang Hu.
Software: Qiang Hu.
Writing – original draft: Xiyin Yang, Qiang Hu.
Writing – review & editing: Xiyin Yang, Qiang Hu.
Abbreviations:
- BC
- breast cancer
- CRP
- C-reactive protein
- GWAS
- genome-wide association study
- IL-6
- interleukin-6
- IVW
- inverse variance weighted
- MR
- Mendelian randomization
- PCT
- procalcitonin
- SAA
- serum amyloid A
- SNPs
- single nucleotide polymorphisms
This study was funded by Project of Traditional Chinese Medicine (No. 2025ZX009, No. 2024ZL345, No. GZY-ZJ-KJ-23051), Project of Zhejiang Provincial Department of Education (Y202351378).
Our research is an analysis of previously collected data and does not involve human participants or animals. Therefore, ethical approval is not applicable.
The authors have no conflicts of interest to disclose.
All data generated or analyzed during this study are included in this published article [and its supplementary information files].
How to cite this article: Yang X, Hu Q. Dissecting the role of inflammatory biomarkers in breast cancer: Insights from Mendelian randomization. Medicine 2025;104:33(e43732).
References
- [1].Wu Y, Zhou BP. Inflammation: a driving force speeds cancer metastasis. Cell Cycle. 2009;8:3267–73. [DOI] [PMC free article] [PubMed] [Google Scholar]
- [2].Karan D, Dubey S. From inflammation to prostate cancer: the role of inflammasomes. Adv Urol. 2016;2016:3140372. [DOI] [PMC free article] [PubMed] [Google Scholar]
- [3].Shaul ME, Fridlender ZG. Neutrophils as active regulators of the immune system in the tumor microenvironment. J Leukoc Biol. 2017;102:343–9. [DOI] [PubMed] [Google Scholar]
- [4].Wang YA, Jian JW, Hung CF, et al. Germline breast cancer susceptibility gene mutations and breast cancer outcomes. BMC Cancer. 2018;18:315. [DOI] [PMC free article] [PubMed] [Google Scholar]
- [5].Kleibl Z, Kristensen VN. Women at high risk of breast cancer: molecular characteristics, clinical presentation and management. The Breast. 2016;28:136–44. [DOI] [PubMed] [Google Scholar]
- [6].Davey Smith G, Hemani G. Mendelian randomization: genetic anchors for causal inference in epidemiological studies. Hum Mol Genet. 2014;23:R89–98. [DOI] [PMC free article] [PubMed] [Google Scholar]
- [7].Smith GD. Mendelian randomization for strengthening causal inference in observational studies: application to Gene × Environment interactions. Perspect Psychol Sci. 2010;5:527–45. [DOI] [PubMed] [Google Scholar]
- [8].Burgess S, Thompson SG. Interpreting findings from Mendelian randomization using the MR-Egger method. Eur J Epidemiol. 2017;32:377–89. [DOI] [PMC free article] [PubMed] [Google Scholar]
- [9].Katikireddi SV, Green MJ, Taylor AE, Smith GD, Munafò MR. Assessing causal relationships using genetic proxies for exposures: an introduction to Mendelian randomization. Addiction. 2017;113:764–74. [DOI] [PMC free article] [PubMed] [Google Scholar]
- [10].Allin KH, Nordestgaard BG, Flyger H, Bojesen SE. Elevated pre-treatment levels of plasma C-reactive protein are associated with poor prognosis after breast cancer: a cohort study. Breast Cancer Res. 2011;13:R35. [DOI] [PMC free article] [PubMed] [Google Scholar]
- [11].Kaur RP, Rubal, Banipal RPS, Vashistha R, Dhiman M, Munshi A. Association of elevated levels of C-reactive protein with breast cancer, breast cancer subtypes, and poor outcome. Curr Probl Cancer. 2019;43:123–9. [DOI] [PubMed] [Google Scholar]
- [12].Hu J, Luo Z, Song J, et al. High C-reactive protein is associated with the efficacy of neoadjuvant chemotherapy for hormone receptor-positive breast cancer. Medicine (Baltim). 2024;103:e40775. [DOI] [PMC free article] [PubMed] [Google Scholar]
- [13].Malik S, Waquar S, Idrees N, Malik A. Impending role of inflammatory markers and their specificity and sensitivity in breast cancer patients. Sci Rep. 2024;14:13117. [DOI] [PMC free article] [PubMed] [Google Scholar]
- [14].Bera A, Russ E, Manoharan MS, et al. Proteomic analysis of inflammatory biomarkers associated with breast cancer recurrence. Mil Med. 2020;185:669–75. [DOI] [PubMed] [Google Scholar]
- [15].Radharani NNV, Yadav AS, Nimma R, et al. Tumor-associated macrophage derived IL-6 enriches cancer stem cell population and promotes breast tumor progression via Stat-3 pathway. Cancer Cell Int. 2022;22:122. [DOI] [PMC free article] [PubMed] [Google Scholar]
- [16].Jia Y, Peng Z, Tian X, et al. Single-cell sequencing exposes mast cell-derived CD52’s anti-tumor action in breast cancer through the IL-6/JAK/STAT3 axis. Int J Biol Macromol. 2025;310:142879. [DOI] [PubMed] [Google Scholar]
- [17].Ibrahim SA, El-Ghonaimy EA, Hassan H, et al. Hormonal-receptor positive breast cancer: IL-6 augments invasion and lymph node metastasis via stimulating cathepsin B expression. J Adv Res. 2016;7:661–70. [DOI] [PMC free article] [PubMed] [Google Scholar]
- [18].Hou L, Xie S, Li G, et al. IL-6 triggers the migration and invasion of oestrogen receptor-negative breast cancer cells via regulation of hippo pathways. Basic Clin Pharmacol Toxicol. 2018;123:549–57. [DOI] [PubMed] [Google Scholar]
- [19].He JY, Wei XH, Li SJ, et al. Adipocyte-derived IL-6 and leptin promote breast Cancer metastasis via upregulation of Lysyl Hydroxylase-2 expression. Cell Commun Signal. 2018;16:100. [DOI] [PMC free article] [PubMed] [Google Scholar]
- [20].Nyati KK, Hashimoto S, Singh SK, et al. The novel long noncoding RNA AU021063, induced by IL-6/Arid5a signaling, exacerbates breast cancer invasion and metastasis by stabilizing Trib3 and activating the Mek/Erk pathway. Cancer Lett. 2021;520:295–306. [DOI] [PubMed] [Google Scholar]
- [21].Bobin-Dubigeon C, Lefrançois A, Classe JM, Joalland MP, Bard JM. Paired measurement of serum amyloid A (SAA) and paraoxonase 1 (PON1) as useful markers in breast cancer recurrence. Clin Biochem. 2015;48:1181–3. [DOI] [PubMed] [Google Scholar]
- [22].Gunaldi M, Okuturlar Y, Gedikbasi A, Akarsu C, Karabulut M, Kural A. Diagnostic importance of S100A9 and S100A12 in breast cancer. Biomed Pharmacother. 2015;76:52–6. [DOI] [PubMed] [Google Scholar]
- [23].Dowling P, Clarke C, Hennessy K, et al. Analysis of acute-phase proteins, AHSG, C3, CLI, HP and SAA, reveals distinctive expression patterns associated with breast, colorectal and lung cancer. Int J Cancer. 2011;131:911–23. [DOI] [PubMed] [Google Scholar]
- [24].Sung HJ, Ahn JM, Yoon YH, et al. Identification and validation of SAA as a potential lung cancer biomarker and its involvement in metastatic pathogenesis of lung cancer. J Proteome Res. 2010;10:1383–95. [DOI] [PubMed] [Google Scholar]
- [25].Levacher C, Viennot M, Drouet A, et al. Disequilibrium between BRCA1 and BRCA2 circular and messenger RNAs plays a role in breast cancer. Cancers. 2023;15:2176. [DOI] [PMC free article] [PubMed] [Google Scholar]