Objective:

To examine fluctuations in peripheral blood lymphocyte subsets in metastatic osteosarcoma patients undergoing immune checkpoint inhibitor therapy, emphasizing the significance of identifying potential biomarkers for treatment response and prognosis.

Key Findings:

• Pre-ICIs CD8+HLA-DR+ cells and post-ICIs CD3−CD56+, CD3+CD4+, and CD8+HLA-DR+ cells were indicators associated with improved overall survival.
• Patients achieving disease control had significantly higher counts of CD45+, CD3−CD56+, CD4+HLA-DR+, CD3+CD8+, and CD8+HLA-DR+ at diagnosis.
• Dynamic increases in post-ICIs CD3−CD56+ and CD8+HLA-DR+ cells correlated with improved treatment response.
• Extrapulmonary metastasis was identified as a significant risk factor for unfavorable overall survival.

Interpretation:

Increased levels and dynamic changes in specific peripheral blood lymphocyte subsets post-ICIs are associated with better overall survival and treatment response in metastatic osteosarcoma patients, with implications for clinical practice.

Limitations:

• Small sample size of 14 patients limits generalizability.
• Retrospective design may introduce bias affecting data reliability.

Conclusion:

This study highlights the potential of peripheral blood lymphocyte subsets as non-invasive biomarkers for predicting ICI efficacy and guiding personalized treatment in metastatic osteosarcoma, warranting further validation in larger cohorts to confirm these findings.