Organ-Specific Differences in Immunotherapy Response Among Metastatic Cancer Patients

Inclusion Criteria:

• Age ≥18 years.
• Pathologically confirmed solid tumor with a documented primary tumor site.
• At least one metastatic site in the brain, liver, lung, or bone confirmed by imaging or pathology (single or multiple lesions allowed).
• Received first-line or second-line immune checkpoint inhibitor (ICB) therapy, including PD-1, PD-L1, or CTLA-4 inhibitors, either alone or in combination.
• Completed at least 3 cycles of ICB therapy.
• At least one evaluable imaging follow-up after initiation of immunotherapy.
• Available clinical and follow-up data, including treatment initiation date, response assessment, progression status, and survival status.
• Meets institutional ethics requirements for retrospective studies.

Exclusion Criteria:

• Unclear or undocumented metastatic site, or lack of imaging/pathologic evidence supporting metastasis.
• ICB treatment regimen cannot be clearly determined (e.g., unclear combination therapy components).
• Missing more than 20% of key clinical variables or incomplete follow-up data (e.g., missing PFS or OS information).
• Received fewer than 3 cycles of ICB therapy.
• Major treatment interruption or poor treatment adherence.
• Concurrent active malignancy that may interfere with outcome assessment.
• Severe immune-related disease (e.g., systemic lupus erythematosus) or organ transplantation requiring long-term immunosuppression.
• Participation in another interventional clinical trial that may affect treatment evaluation.
• Data errors or logical inconsistencies that cannot be resolved after review.