This is an observational cohort study evaluating clinical and pathological outcomes in patients with high-risk stage II melanoma.

Patients are included after receiving treatment as part of routine clinical practice. Decisions about treatment, including whether to start anti-PD1 therapy before surgery, are made by the treating physician and are not influenced by the study.

The study compares outcomes between patients who started anti-PD1 therapy before surgery and those treated according to the usual timing in clinical practice.

No treatments are assigned as part of the study.

This study evaluates the association between the timing of anti-PD1 therapy initiation and clinical outcomes in patients with high-risk stage II melanoma (stages IIB and IIC) and/or microsatellitosis.

The study is designed as an ambispective observational cohort, including both retrospective and prospective patients treated in routine clinical practice.

The retrospective cohort includes patients who were managed according to standard clinical practice, typically undergoing surgical treatment followed by systemic/adjuvant anti-PD1 therapy. The prospective cohort includes patients who initiated anti-PD1 therapy prior to surgery, based on the treating physician's clinical judgment.

All treatment decisions, including the timing of systemic therapy initiation, are made independently by the treating physician and are not influenced by the study protocol. No interventions are assigned as part of the study, and no experimental treatment strategies are implemented.

Patients are categorized according to the timing of anti-PD1 therapy initiation (before surgery or according to standard timing), and outcomes are compared descriptively between these groups.

The study aims to explore whether early initiation of systemic therapy in routine clinical practice is associated with differences in time to treatment initiation and key clinical outcomes, including recurrence-free survival, overall survival, and pathological response.

Given its observational design, the study does not aim to establish causality but rather to generate real-world evidence regarding the potential impact of early anti-PD1 therapy in this high-risk population. As a non-randomized observational study, the results may be subject to confounding factors and selection bias inherent to real-world clinical practice.

Inclusion Criteria:

- Adults (≥18 years) with histologically confirmed cutaneous melanoma stage IIB or IIC or stage III (N1c), managed in routine clinical practice.

Exclusion Criteria:

• Patients without sufficient clinical or follow-up data.
• Patients who do not provide informed consent (for prospective cohort).

Adult patients with high-risk stage II cutaneous melanoma (stages IIB and IIC) and/or microsatellitosis treated in routine clinical practice.