Abstract PO1-22-08: Ductal Lavage versus Oral Corticosteroids in Patients with Idiopathic Granulomatous Mastitis: A Multicenter, Open-label, Randomized, Controlled, Non-inferiority Study

Abstract Background: Idiopathic granulomatous mastitis (IGM) is an inflammatory breast disease characterized by the presence of mass, erythema and fistula. Various treatments have been proposed, including steroids, surgery, immunosuppressants, and observation alone. However, most of the reported studies are single-center, retrospective, single-arm with limited sample sizes, leaving the optimal treatment strategy unknown. In a previous single-arm study, we reported the efficacy and safety of ductal lavage as a novel treatment. This presentation presents the results of a multicenter, open-label, randomized controlled, non-inferiority trial that compares the efficacy and safety of ductal lavage with oral corticosteroids as the first-line treatment for IGM patients. Methods: Eligible IGM patients were randomized 1:1 to receive either ductal lavage or oral corticosteroids, stratified by M-score status. The M-score quantitatively evaluates IGM symptom severity as reported in our previous studies. Ductal lavage involved the intraductal infusion of lidocaine, triamcinolone acetonide, and ceftriaxone with saline, a total 5 times within 2 weeks. Oral corticosteroids were administered using prednisone or methylprednisolone at an initial dose of 20-40mg per day, decreased by 5mg every 2 weeks, and then maintained at 20mg per day for at least 1 month. The primary outcome was the rate of complete Clinical Response (cCR), which was defined as achieving M-score≤1 during any follow-up visit. Secondary outcomes included median time to first cCR, treatment failure, relapse, adverse events, and protocol compliance rate. If the lower limit of 95%CI of the absolute difference between ductal lavage and oral corticosteroids was greater than -15%, the non-inferiority was met. This trial was approved by the ethical committee of Sun Yat-sen Memorial Hospital and registered with ClinicalTrials.gov (NCT03724903). Results: Recruitment for this trial began in March 2019 and follow-up ended in May 2023 at 3 hospitals in China. In the intention-to-treat set (N=140), 69 patients were randomly assigned to the ductal lavage group and 71 patients to the oral corticosteroids group. The cCR rates after treatment were 85.51% (95% CI 77.20 ~ 93.81%) and 87.32% (95% CI 79.59 ~ 95.06%) in the ductal lavage and oral corticosteroids groups, respectively. The rate difference was -1.82% (95% CI -13.17 ~ 9.54%), not exceeding the non-inferiority margin (Non-inferiority P=0.011). In the per-protocol set (N=111), the cCR rate difference was -5.32%(ductal lavage: 92.86% vs. oral corticosteroids: 98.18%),with a 95%CI of -12.94% to 2.29%,also not exceeding the non-inferiority margin(Non-inferiority P=0.006).No significant differences were observed between groups in median time to first cCR (34.0 vs. 32.5 days, P= 0.878), treatment failure rate (14.49% vs. 11.27%, P=0.569), or relapse rate (10.14% vs. 4.23%, P=0.302).In the safety analysis set (N=129), the most frequently reported adverse events ( >15%) in the ductal lavage group were irregular menstruation (46.27%), while in the oral corticosteroids group, they were Cushingoid (79.03%), epigastric pain (17.74%), and arthralgia (16.13%). Conclusions: Ductal lavage demonstrates non-inferiority to oral corticosteroids in terms of efficacy as a first-line treatment for IGM patients. Furthermore, ductal lavage exhibits a significantly favorable adverse events profile. Primary endpoint in ITT and PP set *P value for non-inferiority comparison. Secondary endpoint in PP set §P value calculated by chi-square test. Adverse event in safety set No adverse event exceeding Grade3 have been recorded. Citation Format: Kai Chen, Xiaolin Chen, Shunrong Li, Liling Zhu, Jian Zhang, Tingting Hu, Hui Huang, Heng Huang, Lili Chen, Qiaozhen Xiao, Linhong Su. Ductal Lavage versus Oral Corticosteroids in Patients with Idiopathic Granulomatous Mastitis: A Multicenter, Open-label, Randomized, Controlled, Non-inferiority Study [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-22-08.