Abstract
OBJECTIVES: (1) To assess the risk of haematological malignancies in individuals with systemic sclerosis (SSc) compared with individuals without SSc; (2) to explore how the risk varies across groups stratified by sex and age; and (3) to determine when these malignancies present in relation to SSc diagnosis in a population-based setting. METHODS: We performed a nationwide cohort study using high-quality administrative healthcare registers covering virtually all Swedish residents. All individuals with SSc diagnosed during 2004-2019 and matched general population comparators were included. We identified all haematological malignancies in the study population using the Swedish Cancer Register and estimated the incidence rates using Poisson regression and the HRs using flexible parametric models. We stratified by sex and age and explored the incidence over time since SSc diagnosis. RESULTS: We observed 1720 individuals with incident SSc and 16 983 comparators for 11 480 and 131 021 person-years, respectively. Individuals with SSc had a higher risk of haematological malignancies compared with individuals without SSc (HR 2.2, 95% CI 1.4 to 3.1), especially B-cell malignancies (HR 3.0, 95% CI 1.7 to 4.8). The incidence rate and the HR were highest in men. The SSc over-representation of haematological malignancies was most evident in individuals aged 18-49 years at SSc diagnosis. Myeloid malignancies presented around SSc diagnosis (median 0.1 (IQR 8.2) years after SSc diagnosis) while lymphoid malignancies presented a few years later (median 3.1 (IQR 9.5)). CONCLUSION: Individuals with SSc are afflicted by an increased risk of haematological malignancies, especially B-cell malignancies. The risk is highest in men. Myeloid malignancies tend to present closer to SSc diagnosis than lymphoid malignancies.