Mastitis as a risk factor for breast cancer: a systematic review and meta-analysis

BACKGROUND: Breast cancer (BC) is the most common cancer among women worldwide, accounting for more than 2.3 million new cases annually. Although chronic inflammation is a well-established risk factor for cancer, the association between mastitis and BC has not yet been clearly established. Therefore, this study aims to investigate mastitis as a potential risk factor for BC. METHODS: We performed a random-effects meta-analysis to estimate the odds ratio (OR) and hazard ratio (HR). P values lower than 0.05 were considered statistically significant, with 95% confidence intervals (CI). Statistical analyses were conducted using R Studio software version 4.4.2, considering P < 0.05 as statistically significant. RESULTS: Our meta-analysis included 54,216 patients, of whom 18,753 (34.6%) had mastitis, while 35,463 (65.4%) comprised the control group. Our results support that the risk of BC is higher among patients with a history of mastitis (OR: 2.12; 95% CI: 1.44-3.11; p = 0.0423). Similarly, longitudinal analysis based on total follow-up also confirmed an increased risk of BC in the mastitis group (HR: 2.0057; 95% CI: 1.1739-3.4269; p = 0.011). CONCLUSION: This meta-analysis highlights a possible association between the presence of mastitis and BC, substantially contributing to the advancement of understanding regarding risk factors for this cancer. Prospective studies using robust detection methods and paired tissue analyses are needed to confirm these findings and clarify the role of mastitis in breast tumorigenesis.