Comorbidities in the Spondyloarthritis GISEA Cohort: an average treatment effect analysis on patients treated with bDMARDs

Objectives: We aimed to investigate the effectiveness of tumour necrosis factor inhibitors (TNFi), anti-interleukin-17 or interleukin-12/23 monoclonal antibodies (anti-IL) on comorbidities in a cohort of patients with spondyloarthritis (SpA), using an average treatment effect (ATE) analysis. Methods: SpA patients from the multicentre Italian GISEA Registry were divided into groups according to pharmacological exposure: no treatment (G0), TNFi (G1) and non-responders to TNFi switched to anti-IL (G2). In each group, we recorded the prevalence and incidence of infectious, cardiopulmonary, endocrinological, gastrointestinal, oncologic, renal and neurologic comorbidities. Each comorbidity was then fitted for ATE and baseline features were evaluated for importance. Results: The main findings of this study comprising 4458 SpA patients relate to cancer, other gastrointestinal diseases (OGID) and fibromyalgia. ATE showed no increased risk of solid cancer in G1 (0.42 95% CI 0.20-0.85) and G2 (0.26 95% CI 0.08-0.71) vs. G0, with significantly higher incidence in G0 (14.07/1000 patient-years, p=0.0001). Conversely, a significantly higher risk of OGID and fibromyalgia was found in G1 (1.56 95% CI 1.06-2.33; 1.69 95% CI 1.05-2.68, respectively) and G2 (1.91 95% CI 1.05-3.24; 2.13 95% CI 1.14-3.41, respectively) vs. G0. No treatment risk reduction was observed in haematological malignancies, cardiovascular events and endocrinological comorbidities. Conclusions: Overall, our study confirms the safety of TNFi and anti-IL in SpA patients, albeit with some caveats pertaining to solid cancers, OGID and fibromyalgia. Furthermore, taking into consideration causality with observational data may yield more reliable and relevant clinical information.