Inclusion Criteria:

• Adults, ≥ 18 years of age.
• For rheumatoid arthritis patients:
  • 2010 EULAR/ACR classification criteria of RA.
• For cancer patients on ICI therapy without irAEs, they will be matched to our existing IA-irAE patients by age, sex, cancer types and ICI treatment.

Exclusion Criteria:

• < 18 years of age.
• For rheumatoid arthritis cohort:
  • Active infection;
  • Pregnancy;
  • Any cancer diagnosis;
  • Treatment with biologics;
  • Active use of high dose (≥ 30 mg daily) of prednisone or steroid equivalent;
  • Clinical features suggestive of other non-RA rheumatic disease (e.g., psoriatic arthritis, reactive arthritis, ankylosing spondylitis, lupus, Sjogren’s, , etc) or axial spondyloarthropathy.
• For cancer patient control cohort:
  • No irAE ≤ 6 months following final ICI treatment.