From hypothesis to robust evidence in a nationwide multicenter case–control study on 1490 women: milk stasis and idiopathic granulomatous mastitis

Idiopathic granulomatous mastitis (IGM) is rare globally and infrequent in some middle-east regions. Sex-hormonal factors have been mentioned as predisposing factors for IGM, recent large-sale studies indicate a 7.5-fold increased risk in women who have breastfed. This study investigates BF-related factors that contribute to IGM development. We conducted a multicenter case-control study and recorder BF-related events in 730 IGM patients and healthy 760 controls. The mean age of participants was 36.63 ± 6.49 in the Case and 36.96 ± 6.11 years in the Control Group (p = 0.31). IGM occurred more frequently in the contralateral breast in one-sided BF (p < 0.001), with discordance between the affected side and BF side in 68.3% of cases (p = 0.005). Multivariate analysis revealed significant associations between IGM and one-sided BF (OR = 4.21), post-weaning breast engorgement (OR = 3.06), lactational mastitis (OR = 1.93), and oral medication use for infants (OR = 2.59). The study achieved 100% statistical power for both primary and secondary objectives, with narrow confidence intervals indicating high precision. This study provides robust evidence supporting the milk stasis hypothesis, demonstrating that BF-related issues leading to milk stasis are strongly associated with IGM development. Preventive strategies to minimize milk stasis and encourage bilateral BF may help reduce IGM risk.