**1. Introduction**

Sjögren's syndrome (SS) is the second most common autoimmune disease; it is usually classified as primary or secondary to rheumatoid arthritis and other autoimmune diseases, such as lupus erythematosus, sclerodermia, vasculitis, etc., mainly involves the exocrine glands (salivary and lacrimal glands) and is characterized by progressive infiltration of T-and B-lymphocytes [1,2]. The common detectability of hyper-gamma-globulinemia and different autoantibodies (such as rheumatoid factor, anti-Sjögren's syndrome A and B antibodies) in the blood of SS patients underlines the relevance of B-cell hyperactivity in the pathogenesis [2,3]. Common clinical findings in SS patients are

kerato-conjunctivitis sicca, xerostomia, angular cheilitis, and additional symptoms related to the qualitative/quantitative reduction of exocrine secretions [3]. Along with dryness, SS patients may show disabling symptoms, such as fatigue and pain, but also develop systemic manifestations in up to 30–50% of cases, including renal, lung, or neurological disorders [4,5]. In addition, SS patients have an increased risk of lymphoma, such as marginal zone lymphoma (MZL) or mucosal-associated lymphoid tissue (MALT) lymphoma [6–10]. The World Health Organization in 2016 classified MZLs into three distinct types, according to the involved sites: extranodal MZL of MALT (generally termed as MALT lymphoma), nodal MZL, and splenic MZL [11].

The worldwide incidence of SS is difficult to assess as many cases remain undiagnosed for years [12,13]. Overall, extranodal MALT lymphomas more frequently affect the stomach, spleen, thyroid, ocular adnexal tissues, and salivary glands, while they are rare in the breast (1.7–2.2% of primary breast lymphomas), possibly due to the anecdotic presence of MALT tissue at this site [14,15].

Moreover, SS patients may be affected by non-Hodgkin lymphomas (NHL) over the course of the disease; less than 20% are diffuse B-cell lymphomas while the most frequent are of the MALT type (up to 60%), the latter more commonly involving the minor and major salivary glands, pharynx, stomach, small intestine, and thyroid, with an incidence 10–44 times higher than in the general population [4,5,8–10,16,17].

We report on a case of an extranodal marginal zone lymphoma of MALT, occurring in the breast of a Caucasian woman, with a three-year history of Sjögren's syndrome; also, data from the literature on this topic have been collected and reviewed.
