Demographic and clinical characteristics of each case
| Patient | 1 | 2 | 3 |
| Age, years | 71 | 65 | 46 |
| Sex | Male | Male | Female |
| Race | Caucasian | Caucasian | Caucasian |
| Tumour | Metastatic melanoma | Metastatic melanoma | Metastatic melanoma |
| ICIs | Ipilimumab | First: Ipilimumab Second: Pembrolizumab | First: Pembrolizumab Second: Ipilimumab |
| Tumour response to ICIs at present (RECIST 1.1) | Complete remission | Progressive disease | Progressive disease |
| Onset of arthritis irAEs | After the fourth infusion | After the second infusion of pembrolizumab | After the third infusion of Pembrolizumab |
| Pattern of arthritis | Symmetric polyarthritis involving small joints | Symmetric polyarthritis involving small and large joints | Symmetric polyarthritis involving small joints |
| Autoantibody results | ANA, CCP neg RF: 27 IU/ml (UNL: 15.9 IU/ml) | ANA, CCP, RF neg | CCP, RF, Ro, dsDNA neg ANA 1:640 (homogenous) La positive |
| Duration of tocilizumab (months) | 11 (ongoing) | 15 (ongoing) | 3 (discontinued) |
ANA, antinuclear antibody; CCP, anti-cyclin citrullinated antibody; dsDNA, anti–double-stranded DNA antibody; ICI, immune checkpoint inhibitor; La, anti-SSB antibody; RF, rheumatoid factor; Ro, anti-SSA antibody; UNL, upper normal limit.