GRAnulomatous MAstitis REGistry Study

Overview

Idiopathic granulomatous mastitis (IGM) is a rare benign inflammatory breast condition with unknown cause, affecting approximately 2.4 per 100,000 women aged 20-40 years. Patients experience severe local symptoms including pain, redness, and recurrent abscesses that can last weeks to months and often mimic inflammatory breast cancer. Due to its rarity, mostly case reports and case series exist in the literature, leading to limited knowledge about risk factors, optimal treatment strategies, and clinical outcomes. The GRAMAREG study is the first European registry for patients with histologically confirmed idiopathic granulomatous mastitis. This retrospective/prospective observational cohort study aims to systematically evaluate the incidence, diagnostic features, clinical course, treatment strategies, and patient outcomes of this uncommon disease. The study collects both retrospective data (from January 1, 2015 onwards) and prospective data from participating sites across Europe. All diagnostic and therapeutic procedures are conducted according to institutional standards in clinical routine, as this is a non-interventional study. Patients in the prospective cohort are followed for up to 5 years to document symptom duration and recurrence rates.

Background: Idiopathic granulomatous mastitis was first described by Kessler and Wolloch in 1972. The etiology remains largely unknown due to its rare occurrence. Valid prevalence data in Europe are lacking, though incidence appears higher in low-income countries compared to Western Europe. IGM predominantly occurs in women of childbearing age, mostly parous and more frequently of non-white ethnicity. The diagnosis is confirmed only by histological evaluation, typically using core needle biopsy. Patients commonly develop recurrent breast abscesses that do not improve with antibacterial medication and often require repeat incisions or drainages. IGM must be differentiated from granulomatous inflammation associated with duct ectasia, foreign material reactions, specific infections (tuberculosis, fungi, parasites), systemic granulomatous diseases (sarcoidosis), and cystic neutrophilic granulomatous mastitis (CNGM) linked to Corynebacterium species. Treatment strategies described in literature include high-dose steroids, immunosuppressive agents, bromocriptine, antibiotics, surgical resection, or even mastectomy. However, no evidence-based treatment recommendations are currently available. Study Design: This is an investigator-initiated non-interventional observational international prospective/retrospective cohort study with unlimited accrual and open registry duration due to disease rarity. Data Collection Methods: Retrospective Phase: Collection and analysis via anonymized electronic database maintained by EUBREAST e.V. Participating Study Sites identify and document patients with histologically confirmed IGM treated between January 1, 2015, and Study Site activation. No patient identifying information is disclosed or documented. Data are fully anonymous without prospective follow-up. Prospective Phase: Patients with histologically confirmed IGM presenting after Study Site activation are informed about possible participation. Written informed consent is obtained. Diagnostic management and treatment follow institutional standards without protocol deviation. Follow-up occurs at 1, 3, and 5 years after first diagnosis to evaluate current symptoms and document potential recurrence.