Study population

Patients are eligible for this study when the following inclusion criteria are met:

age ≥ 18 year

advanced or metastatic cutaneous melanoma

current monotherapy with first-line nivolumab or pembrolizumab for advanced or metastatic melanoma; previous systemic treatment, including immunotherapy, in (neo) adjuvant setting for resectable melanoma is allowed

documented diagnostic CT or MRI at the start of PD-1 blockade with nivolumab or pembrolizumab

for patients with CR on a diagnostic CT at response evaluation, a low-dose CT (i.e. usually included for positron emission tomography [PET] using fluorine-18 fluorodeoxyglucose [¹⁸F-FDG]) is allowed at baseline

for patients with PR on a diagnostic CT at response evaluation, a low-dose CT (i.e. usually included for ¹⁸F-FDG PET) is allowed at baseline if sufficient target lesions are measurable for response evaluation according to RECIST v1.1 criteria [34]; in this specific case, the sponsor should be consulted

documented tumour response evaluation every 12 ± 1 weeks according to RECIST v1.1 [34] using a diagnostic CT and/or MRI as per standard clinical practice

having confirmed CR (with an interval of 6–12 [+ 1] weeks after first documentation) or an ongoing PR (with an interval of 12 [±1] weeks after first documentation) according to RECIST v1.1 [34] using a diagnostic CT and/or MRI

presence of MRI brain for the screening of brain metastases (prior to first start or discontinuation of PD-1 blockade)

planned and willing to discontinue nivolumab or pembrolizumab within 6 (+ 1) weeks after first confirmation of CR or PR and within 2 years from initiation of treatment

signed and dated informed consent form

A potential subject who meets the following criterion will be excluded from participation in this study:

concomitant systemic therapies with other anti-cancer agents, e.g. BRAF-inhibitor, anti-CTLA4 (e.g. ipilimumab), or other PD-1 blockade than nivolumab or pembrolizumab