Skin rash during tumor treatment with immunotherapy (anti-PD1 antibody therapy) is a common side effect. If patients suffer from such a skin reaction, they typically suffer from a rash on the chest, back and extremities. The skin reaction is usually treated with cortisone in cream or tablet form. There is already research in humans on the skin reaction under anti-PD1 antibody therapy. Previous studies in humans have shown that certain inflammatory markers are elevated. It is also know that the study drug can help to reduce these inflammatory markers. However, there is currently not enough data available whether the study drug can actually reduce inflammation in the skin in a rash under anti-PD1 antibody therapy. The investigators are therefore examining in this study whether the study drug is effective and well tolerated in a skin rash under anti-PD1 antibody therapy. The study drug contains the active ingredient ruxolitinib and is applied as a cream. The study drug is approved for other skin diseases (vitiligo and atopic eczema) in the USA and in countries of the European Union (EU). Approval in Switzerland is still pending. Only once the efficacy of the study drug against skin rashes under anti-PD1 antibody therapy has been scientifically investigated and proven can it be approved and used as a therapy in Switzerland. In this study, the participants are not divided into groups. Each study patient receives the test substance.

Inclusion Criteria:

Adult patients eligible for this inclusion in this study have to fulfil all the following criteria:

• Indication: lichenoid skin toxicities / rash which has developed under / after anti-PD-1 therapy.
• Male and Female patients ≥18 years of age
• Patients that are able to speak and read German or English.
• The subject was informed and gave his/her consent to the Institutional Review Boards (IRB)/Independent Ethics Committee (IEC) -approved informed consent

Exclusion Criteria:

Patients fulfilling any of the following criteria are not eligible for the inclusion in this study:

• Patient suffering other skin disease resembling lichenoid skin lesions under anti-PD-1 therapy.

• Acute psychiatric illness or acute crisis.

• Contraindications to ruxolitinib, e.g. known hypersensitivity or allergy

• Topical glucocorticosteroids, topical calcineurin inhibitors and UV light therapy are not allowed during the study or for 1 week before the study beginning. Other JAK inhibitors or potent immunosuppressants such as azathioprine or cyclosporine are not allowed during the study or for 8 weeks before the study beginning.

• Women who are pregnant or breast feeding *

• Intention to become pregnant during the course of the study

• Known or suspected non-compliance, drug or alcohol abuse.

• Patients with an active, serious infection, including localized infections.

• Inability to follow the procedures of the study due to language problems, psychological disorders, dementia of the participant.

• Participation in another study with topical or oral ruxolitinib within the 30 days preceding and during the present study.

• Previous enrolment into the current study.

• Enrolment of the investigator, his/her family members, employees and other dependent persons.

  • Participants must avoid pregnancy during the study. A blood pregnancy test is required before start of therapy, with regular urine tests throughout. Lactating individuals are ineligible.

Participants must use effective contraceptives, either:

• An ovulation-inhibiting method (e.g., pill, injectable, implant, patch, or vaginal ring) or
• An intrauterine device (IUD).
• Contraception should extend one week post-study. If pregnancy occurs during or within one week after the study, participants should notify the overseeing physician immediately.