The study is designed as a prospective, single-arm observational, mixed-method study. Patients with stage IV NSCLC or inoperable mesothelioma will be included and will be treated with immunotherapy according to current guidelines and standard of care. Patients may receive either a PD1/L1 inhibitor monotherapy or, if indicated, together with a CTLA4 inhibitor. Immunotherapy may be administered alone or together with chemotherapy as per site standard/physician's choice. Patients will be given access to a mobile app. Patients will receive daily questions via the app to assess immune-related adverse events between clinic visits and their well-being.

Inclusion Criteria:

• Signed Informed Consent Form
• Age > 18 years at the time of study entry
• Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 2
• Life expectancy > 6 months
• Patient is able and willing to use smart phone and a wearable device/technology/sensor

Exclusion Criteria:

• Previous systemic treatment for metastatic or locally advanced disease

Cohort 1: Double immune checkpoint inhibition

• Histologically or cytologically confirmed stage IV NSCLC without EGFR sensitizing mutations or ALK translocations OR
• Histologically or cytologically confirmed advanced, malignant pleural mesothelioma
• Eligible for double immune checkpoint inhibition with an anti PD1/L1 inhibitor and a CTLA-4 inhibitor with or without chemotherapy according to current guidelines and SmPCs

Cohort 2: Immunotherapy with PD1/L1 inhibitor:

• Histologically or cytologically confirmed stage IV NSCLC without EGFR sensitizing mutations or ALK translocations
• Eligible for treatment with an anti-PD-1/L1 inhibitor with or without chemotherapy according to current guidelines and SmPCs