It is well-known that patients with rheumatoid arthritis (RA) experience an increased risk of cancer compared with the general population. Potential carcinogenic risk factors in patients with RA include chronic inflammation, lifestyle factors, and use of immunosuppressive drugs (ISDs). The cancer-related concern on use of ISDs pertain to the important function of the immune system in keeping aberrant cells at bay, and potentially suppressing the immune system’s ability to exert such important function might cause an increased cancer risk. In patients with RA, these concerns particularly relate to the newer so-called 'biological' drugs and the synthetically targeted janus kinase inhibitors (JAKi), where knowledge regarding many aspects of cancer risk remains limited.

This PhD thesis encompasses three separate studies based on Danish registry data. The first two studies investigated the risk of primary cancer in patients with RA who received treatment with: 1) Tocilizumab/Sarilumab, Rituximab, or Abatacept, and 2) JAKi, respectively. The third study looked into the risk of cancer recurrence in RA patients with a history of cancer in remission, who then received biological treatment for their RA.

Overall, the PhD thesis shed light on different aspects of cancer risk with biological and JAKi treatment in patients with RA. No indications of increased risks of primary cancer with the biologics Tocilizumab/Sarilumab, Rituximab, or Abatacept were found, nor for treatment with JAKi. However, certain risk signals for abatacept and JAKi warrant additional studies on the topic. Findings from study 3 also indicate that biologics as used in clinical practice in patients with RA and a history of cancer were not associated with an increased risk of cancer recurrence—at least for specific solid cancers in remission and when using Tumor Necrosis Factor Inhibitors or Rituximab.

Hopefully, the results from these three studies and this PhD thesis can contribute with knowledge about important rheumatic drugs in relation to cancer risk, benefiting both doctors and patients.