Effective treatment of steroid‐resistant immune checkpoint inhibitor pneumonitis with mycophenolate mofetil

Abstract Insufficient evidence is available for treating steroid‐resistant immune checkpoint inhibitor pneumonitis (CIP). Although guidelines recommend the use of immunosuppressants, the efficacy of mycophenolate mofetil (MMF) has not been sufficiently verified. We report two cases of steroid‐resistant CIP treated with MMF. Both patients responded to initial treatment with prednisolone (PSL), but the CIP flared up repeatedly as the steroids were gradually tapered off. Upon receiving MMF in addition to PSL, their subjective symptoms improved, and the shadows gradually disappeared, allowing for a reduction in the steroid dose. Ultimately, no CIP recurrence was observed despite discontinuing PSL and MMF. Both cases were completely resolved by treatment with MMF. This indicates that MMF may be effective in treating steroid‐resistant CIP. In the future, the effects and safety of MMF should be investigated in large‐scale clinical trials targeting patients with steroid‐resistant CIP.