Original ArticlesIgG4-related Sclerosing Mastitis: Description of a New Member of the IgG4-related Sclerosing DiseasesCheuk, Wah MBBS*; Chan, Alexander C. L. MBBS*; Lam, Wai-Lung MBBS†; Chow, Sheung-Ming MBChB‡; Crowley, Peter MBBS§; Lloydd, Richard FRCPA∥; Campbell, Ian MBChB¶; Thorburn, Murray MBChB♯; Chan, John K. C. MBBS*Author Information *Department of Pathology ‡Department of Surgery, Queen Elizabeth Hospital †Department of Pathology, Princess Margaret Hospital, Hong Kong §Austin Health, Victoria, Australia ∥Diagnostic Medlab Limited, Auckland ¶Waikato Academic Division, University of Auckland School of Medicine, Hamilton ♯PathLab, Hamilton, New Zealand Correspondence: Wah Cheuk, MBBS, Department of Pathology, Queen Elizabeth Hospital, Wylie Road, Kowloon, Hong Kong (e-mail: firstname.lastname@example.org). The American Journal of Surgical Pathology: July 2009 - Volume 33 - Issue 7 - p 1058-1064 doi: 10.1097/PAS.0b013e3181998cbe Buy Metrics Abstract Immunoglobulin G (IgG)4-related sclerosing disease is a recently described syndrome characterized by mass-forming lesions in various organs due to dense lymphoplasmacytic infiltrates and stromal sclerosis, elevated serum IgG4 titer, increased tissue IgG4+ plasma cells, and favorable clinical outcome. We describe 4 patients with IgG4-related sclerosing mastitis, which represents a new member of this family of diseases. All patients were female with a mean age of 47.5 years, presenting with painless masses in 1 or both breasts. One patient had concurrent IgG4-related lymphadenopathy, and another had eyelid swelling of undetermined cause. The serum IgG4 titer was elevated in 1 tested patient, and circulating autoantibodies were found in 3 tested patients. All patients were well with no recurrence after excision or biopsy of the mass. Histologically, the breast masses featured dense lymphoplasmacytic infiltrates, prominent stromal sclerosis and loss of breast lobules. Phlebitis was present in 1 case. IgG4+ cells ranged from 272 to 495 per high-power field, constituting 49% to 85% of all IgG+ cells. IgG4+ cells were scarce in 9 of 9 cases of lymphocytic mastitis and 6 of 7 cases of granulomatous mastitis studied as controls. In summary, IgG4-related sclerosing mastitis appears to be a distinctive form of mastitis, sometimes accompanied by other components of IgG4-related sclerosing disease, and shows a favorable clinical outcome. © 2009 Lippincott Williams & Wilkins, Inc.