The goal of this clinical trial is to investigate the safety of rituximab for management of immune-related adverse events in malignant melanoma patients. The main questions it aims to answer are:

• Is rituximab safe for management of immune-related adverse events in malingnant melanoma patients?
• Does rituximab provide indications of clinical benefit in the management of immune-related adverse events compared with corticosteroid treatment alone?

Participants will:

• Receive a single dose of 100 mg rituximab IV
• Have regular follow-up consultations for 6 months following rituximab infusion
• Follow a simultaneous corticosteroid tapering plan

Inclusion Criteria:

• Histologically confirmed malignant melanoma diagnosis
• Treatment with immune checkpoint inhibitors (anti-PD1, anti-PDL1, anti-LAG3 and/or anti-CTLA4) due to melanoma within 3 months
• Any irAEs grade 2-4 according to CTCAE v. 6.0
• Negative pregnancy test (serum hCG) in women of childbearing potential
• Age ≥ 18 years
• Ability to provide written and oral consent
• The patient is able to understand and read Danish

Exclusion Criteria:

• Any ongoing infectious disease
• Neutropenia (<1.5 x10^9/L) and/or thrombocytopenia (<75 x10^9/L)
• Known hypersensitivity towards the active substance rituximab or any of the excipients
• History of cardiovascular disease including severe heart failure NYHA grade 3-4, unstable angina pectoris, atrial fibrillation, atrial flutter, and myocardial infarction
• Any major wounds
• Low baseline IgG (<6 g/L)
• Positive hepatitis B virus, hepatitis C virus, HIV, or tuberculosis screening
• Concomitant immunosuppressive medication except prednisolone
• Concomitant chemotherapy or other antineoplastic therapy (except checkpoint inhibitor therapy) within 30 days prior to inclusion
• Females of childbearing potential or males of reproductive potential who are not willing to use an effective method of contraception, such as oral, injected, or implanted hormonal methods of contraception, intrauterine device or intrauterine system, condom in combination with occlusive cap (diaphragm or cervical/vault caps) with spermicidal foam, gel, film, creamor suppository, male sterilization, or true abstinence throughout study and for a minimum of 3 months after study drug therapy.