Efficacy and safety of PD-1/ PD-L1 inhibitors as adjuvants in the treatment of patients with solid cancers: A systematic review and meta-analysis of randomized controlled trials

Maryam Aleid1, Fatimah Aleid1, Daniah Allbdi2, Ahmad Rchdeih3, Dhai Almuteri4, Abdulelah Almesned5, Samaa Alotab6, Yumna AlMishary7, Galia Alsamman8 and Atlal Abusanad2 1 College of Medicine, Imam Abdulrahman Bin Faisal University, Dammam 34212, Eastern Province, Saudi Arabia 2 Faculty of Medicine, King Abdulaziz University, Jeddah 21589, Saudi Arabia 3 Internal Medicine Resident, Royal Commission Hospital, Al-Jubail 31961, Saudi Arabia 4 Internal Medicine Resident, King Fahad Specialist Hospital, Qassim Health Cluster, Buraydah 52366, Saudi Arabia 5 College of Medicine, Qassim University, Unaizah 51911, Saudi Arabia 6 College of Medicine, Alfaisal University, Riyadh 11533, Saudi Arabia 7 College of Medicine, Majmaa University, Riyadh 15341, Saudi Arabia 8 Obstetric and Gynecology Resident, Dr. Suliman Al Habib Women Health, Riyadh 12344, Saudi Arabia Correspondence to: Dhai Almuteri, email:d.almuteri@qu.edu.sa Keywords: PD-1; PD-L1; adjuvant immunotherapy; cancer; solid tumor Received: May 08, 2025     Accepted: February 27, 2026     Published: March 31, 2026 Copyright: © 2026 Aleid et al. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. ABSTRACT Background/Objectives: Programmed cell death protein-1 (PD-1) and programmed death ligand-1 (PD-L1) inhibitors are widely used in cancer treatment. Their benefit as adjuvant therapy in solid tumors is still being defined. This systematic review and meta-analysis evaluated the efficacy and safety of PD-1 and PD-L1 inhibitors as adjuvant treatment in patients with solid tumors. Methods: We conducted a systematic review and meta-analysis of randomized controlled trials in accordance with PRISMA recommendations and PROSPERO registration CRD42024563699. PubMed, Web of Science, Cochrane Library, and Google Scholar were searched for randomized controlled trials published in English that evaluated adjuvant PD-1 or PD-L1 inhibitors in solid cancers. Results: Thirteen randomized controlled trials published between 2021 and 2023 were included. Adjuvant PD-1 and PD-L1 inhibitors improved disease-free survival (hazard ratio 0.75; 95% CI 0.65–0.86) and distant metastasis-free survival (hazard ratio 0.69; 95% CI 0.54–0.87). No clear difference in overall survival was observed. Trial-level subgroup sizes varied across cancer types. Conclusions: Adjuvant PD-1 and PD-L1 inhibitors improve disease-free and distant metastasis-free survival in selected patients with high-risk solid tumors. The clinical benefit must be balanced against higher toxicity rates. Because the number of studies within each cancer type remains limited, the strength of cancer-specific conclusions is restricted, and further research is required.