Background Lupus Mastitis is rare and can be easily confounded with infection or breast cancer.

Methods We report two cases of lupus mastitis, in different clinical settings.

Results The first patient was a 34-year-old female with Systemic Lupus Erythematosus (SLE) with renal, hematological, musculoskeletal and cutaneous involvement, medicated with hydroxychloroquine (HCQ) 400 mg/day, mycophenolate mofetil 2000 mg/day and prednisolone 7.5 mg/day. She presented to the emergency department with painful right breast. On the examination, the breast was swollen, warm and painful to palpation. Breast ultrasound revealed a vascularized and lobulated mass at the upper external quadrant, with liquid areas inside, suggesting possible abscess, which was drained and biopsied.

Histopathological analysis demonstrated a fibroinflammatory process, with fibrotic and abscedated areas, ductitis, lobulitis and vasculitis, compatible with lupus mastitis.

Cultures from the aspirated fluid were negative.

The patient was medicated with antibiotic, NSAIDs and prednisolone dose was increased to 10 mg/day with significant improvement.

The second case refers to a 48-year-old female patient, with SLE with cutaneous, immunological and musculoskeletal involvement, who had withdrawn HCQ due to ocular toxicity. In the following months, the patient presented recurrent episodes of mastitis, on the same location. Breast ultrasound performed during one of the episodes revealed a hyperecogenic area of the fibroglandular tissue, with cystic areas. In spite of repeated treatment with antibiotics and NSAIDs, mastitis recurred, in a total of seven times. Because of worsening of the cutaneous lupus, the patient was medicated with methotrexate up to 15 mg/week. No more episodes of mastitis were recorded and biopsy of the breast, which had been considered, was not performed due to total recovery. The gynecology and rheumatology teams concluded that lupus was the etiology of the recurrent mastitis.

Conclusions Clinicians should be aware of this entity to avoid unnecessary invasive procedures, which may increase inflammation involved in lupus mastitis. Therapeutic approach usually demands increasing immunomodulation.