This study will explore the mechanism of targeted drug in treatment of idiopathic granulomatous mastitis, and clarify the clinical classification and corresponding markers.

This study is aimed to explore the treatment effect of baricitinib in idiopathic granulomatous mastitis (IGM), as well as the clinical classification, potential markers and underline etiology of the disease. The target population of interest in this study is patients with non-lactating mastitis, which require core needle biopsy pathology to indicate mastitis without any pathogen infection. When IGM was diagnosed and informed consent complete, low dose of daily 2mg baricitinib was taken orally as the monotherapy in this trial. Follow-up visits were sheduled at baseline (i.e. pretreatment) , 1,3,6 months after treatment, and then every 3 months thereafter until 2 years after treatment discontinuation when achieving complete response. At each follow-up visit, the biggest IGM lesion in each patient was measured by breast ultrasound and 12 inflammational cytokines in peripheral blood should be tested. The primary end point was the objective response rate (ORR) including clinical complete response rate (CR) and partial response rate (PR), and the secondary end point was the recurrence rate within 12 months after drug discontinuation when achieving CR, the degree of inflammation markers decline, and the toxicity and side effects of the drug.

[Inclusion Criteria]

Patients who are willing to participate in clinical research; females; age 18-70 years; KPS>80%, ECOG<2; non-lactating mastitis; core needle biopsy pathology suggests mastitis or (if there is a palpable lump, biopsy pathology suggests) interstitial chronic cell infiltration. At the same time, the special staining of immunohistochemistry is negative [anti-acid, mucicarmine, PAS, fungi (FISH), TB (FISH), methenamine silver], and the possibility of infection with fungi, Mycobacterium tuberculosis or other rod bacteria is ruled out via DNA sequencing using fresh tissue taken from IGM lesions; measurable lesions (mainly low echo lesions detectable by breast ultrasound).

[Exclusion Criteria]

1. Related to subjects:

   Pregnant, breast-feeding, or women planning to have children within 3 years; informed consent does not meet the requirements (if not the patient herself, authorization consent form is missing).

2. Relevant to the disease:

   Core-needle biopsied pathology suggests inflammation caused by pathogens such as tuberculosis or other bacteria, or any item tested positive in the above immunohistochemistry; lung (HR) CT suggests that tuberculosis or tumor cannot be ruled out; Misdiagnosis; No testing records available; No revisit records available.

3. Exclusion criteria related to concomitant medication:

Unable to conduct an efficacy evaluation due to the use of other potential therapeutic drugs, such as glucocorticoids or antituberculosis drugs; Confirmed malignant tumors, those under treatment or after treatment; With severe complications such as cardiac or pulmonary insufficiency, severe cerebral infarction, etc., unable to tolerate treatment.