American Society of Breast Surgeons, Society of Breast Imaging, and College of American Pathology 2025 Guidelines for the Management of Infectious and Inflammatory Lesions of the Breast

Importance: The management of infectious and inflammatory lesions of the breast remains controversial. The expert panel focused on management recommendations for 3 of the most common infectious breast conditions, as very few evidence-based guidelines for the management of these conditions exist. Observations: Clinicians should distinguish between infectious and noninfectious lactational mastitis (LM) because the former often requires interventions whereas the latter requires supportive care only. Patients with infectious LM often have thick fluid collections that are not amenable to aspiration and usually require a stab incision with drain placement (but no packing) to resolve the infection. Operative drainage is only required if the patient cannot tolerate an office procedure. If a phlegmon is present, antibiotics should be prescribed for at least 10 days. The diagnosis of granulomatous mastitis (GM) requires pathology confirmation with characteristic findings on core biopsy. Cystic neutrophilic granulomatous mastitis (CNGM) is a specific form of GM associated with a granulomatous reaction to Corynebacterium infection and should be empirically treated with doxycycline. For patients without findings characteristic of CNGM and no other associated bacterium identified, there is no role for empiric antibiotic use. Granulomatous mastitis cases often recur and can take up to 18 months to resolve. Patients who have GM cases with worsening symptoms should be treated with repeated intralesional steroid injections; surgical excision or repeated aspirations should be avoided. Cases refractory to intralesional steroid injection may require oral steroids or even advanced biologic agents such as methotrexate or azathioprine. Periductal mastitis with squamous metaplasia of lactiferous ducts (PDM-SMOLD) is a distinct entity from other periductal mastitis cases that can present with recurrent abscesses and should be treated with antibiotics and aspiration for fluid collections. Operative excision for PDM-SMOLD is required for those patients who present with a fistula or recurrent episodes typically using a radial incision to remove the diseased ducts within and below the nipple. Conclusions and Relevance: Evidence-informed, consensus-, and expert opinion-based guidelines for the management of infectious and inflammatory conditions of the breast were developed. Clinicians can use these guidelines to appropriately manage these conditions for which clinical care often varied in the past.