Lymphoma studies in patients with Sjögren's syndrome

Vasaitis, L. 2017. Lymphoma studies in patients with Sjögren's syndrome. Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine 1331. 94 pp. Uppsala: Acta Universitatis Upsaliensis. ISBN 978-91-554-9912-9. Patients with primary Sjögren’s syndrome (pSS) are at increased risk of developing malignant lymphoma. The studies in this thesis aim at broadening our understanding of the association between these two conditions. Germinal centre (GC)-like structures were found in minor salivary gland biopsies taken at the time of pSS diagnosis in 25% of 175 studied patients. Lymphoma development was observed in 86% of the GC-positive pSS patients and 14% of the GC-negative patients. GC-like structures in salivary gland biopsies at pSS diagnosis might identify pSS patients at high risk for later lymphoma development. We used the National Patient Register and the Cancer Register to identify pSS patients with lymphoid malignancy for the following studies. The lymphoma tissues were reviewed and classified according to the WHO classification. In a study of 79 patients with available lymphoma tissues, we identified histopathological and clinical features compatible with IgG4-related disease (IgG4-RD) in one patient (1.3%). Histological features of IgG4-RD in lymphoma tissue in patients with an initial pSS diagnosis seem to be rare but, if present, may indicate underlying IgG4-RD. We identified and compared pSS patients with (n=18/17%) and without (n=87) pre-existing lymphoma at pSS diagnosis and found similar pSS characteristics in both groups. Mucosaassociated lymphoid tissue (MALT) lymphoma in salivary glands was more common in patients with pre-existing lymphoma. The findings support the removal of pre-existing lymphoma as a general exclusion criterion for a pSS diagnosis in classification criteria. Further, the findings suggest an investigation for pSS in patients presenting with MALT lymphoma in salivary glands. We compared the distribution of lymphoma subtypes with a general population reference. Both diffuse large B-cell lymphoma (DLBCL) (32%) and marginal zone lymphoma (MZL) (31%) were common, but only MZL (MALT lymphomas) occurred at an increased relative frequency compared to the general population. Men constituted 15% of 105 pSS patients with lymphoma. Men had a shorter time between the pSS and lymphoma diagnoses and more often had lymphoma in the salivary glands compared with women. Increased awareness of signs of lymphoma in salivary glands already during the first years after pSS diagnosis is justified in men with pSS.