Female cancer incidence before and after diagnosis of primary Sjögren's disease: A retrospective cohort study

In primary Sjögren's disease (pSjD), there is a well-documented increased risk of hematological malignancies, particularly lymphomas, whereas studies examining the incidence of solid tumors have often yielded conflicting results. Data concerning the incidence of breast and gynecological cancers are similarly inconsistent. The aim of this study was to further investigate the incidence of these so-called female cancers by assessing not only their occurrence following the diagnosis of pSjD but also prior to it. By linking the Malmö Sjögren's disease register with the Swedish National Cancer Register, 25 cases of female cancers were identified among patients with pSjD (mean follow-up time: 45.8 years), compared to 50.70 expected cases (SIR, 0.49; 95 % CI, 0.30-0.69; <i>P</i> < 0.001). The incidence of female cancers was significantly reduced both prior to (<i>P</i> < 0.001) and following (<i>P</i> < 0.001) the diagnosis of pSjD. The decrease was most evident for breast cancer (SIR, 0.46; 95 % CI, 0.24-0.69; <i>P</i> < 0.001). A reduction was also noted for ovarian cancer (SIR, 0.21; 95 % CI, 0.00-0.62; <i>P</i> < 0.001); however, the reliability of this estimate is limited by the small number of observed cases. Our findings suggest a reduced risk of female cancers, primarily driven by a decrease in breast cancer incidence, not only following but also preceding the diagnosis of pSjD. These results, combined with the observation that autoantibodies characteristic of pSjD often emerge several years before clinical onset, raise the question of whether an autoimmune component may confer a protective effect against breast cancer in pSjD.