Early observations and pilot data that first suggested a new direction
For decades, advanced melanoma was essentially untreatable, with dacarbazine offering response rates below 15% and no survival benefit. The discovery that tumour cells exploit immune checkpoints — particularly CTLA-4 and PD-1/PD-L1 — to evade immune destruction opened an entirely new therapeutic paradigm. Ipilimumab, a monoclonal antibody blocking CTLA-4, became the first agent to demonstrate an overall survival benefit in metastatic melanoma.
Landmark RCTs and pivotal trials that established the evidence base
The PD-1 inhibitors nivolumab and pembrolizumab demonstrated superior efficacy to ipilimumab with less toxicity. CheckMate 067 established nivolumab plus ipilimumab combination therapy as the most effective regimen, with 5-year overall survival of 52%. KEYNOTE-006 confirmed pembrolizumab's superiority over ipilimumab. Crucially, KEYNOTE-024 extended checkpoint inhibitors beyond melanoma, showing pembrolizumab doubled progression-free survival versus chemotherapy as first-line treatment for PD-L1-high non-small cell lung cancer.
Follow-up studies, subgroup analyses, and real-world validation
Checkpoint inhibitors rapidly expanded to the neoadjuvant setting. CheckMate 816 (2022) demonstrated that adding nivolumab to neoadjuvant chemotherapy for resectable NSCLC increased pathological complete response from 2.2% to 24.0%. KEYNOTE-522 showed similar benefits in triple-negative breast cancer. By 2025, checkpoint inhibitors were approved across more than 15 tumour types, including renal, bladder, head and neck, liver, gastric, and MSI-high cancers regardless of histology.
Integration into clinical practice guidelines and recommendations
NCCN and ESMO guidelines incorporated checkpoint inhibitors as standard of care across melanoma, NSCLC, renal cell carcinoma, urothelial carcinoma, head and neck squamous cell carcinoma, hepatocellular carcinoma, and MSI-high solid tumours. PD-L1 testing and tumour mutational burden became routine biomarkers guiding treatment selection.
NCCN NSCLC Guidelines
Pembrolizumab first-line for PD-L1 ≥50% NSCLC; pembrolizumab + chemo for PD-L1 <50%
ESMO Melanoma Guidelines
Nivolumab + ipilimumab or anti-PD-1 monotherapy as first-line for advanced melanoma
Now
Current standard of care and ongoing research directions
Checkpoint inhibitors are now one of the foundational pillars of medical oncology, used across the full spectrum from neoadjuvant to metastatic settings in over 15 cancer types. Current research focuses on overcoming primary and acquired resistance, optimal combination strategies, predictive biomarkers beyond PD-L1, and managing the growing population of long-term survivors with chronic immune-related adverse events.
Tumour cells exploit immune checkpoints (CTLA-4, PD-1/PD-L1) to suppress T cell activity and evade immune destruction. Checkpoint inhibitors are monoclonal antibodies that block these checkpoints, re-activating the immune system to recognise and attack cancer cells.
Which was the first checkpoint inhibitor to show survival benefit?+
Ipilimumab (anti-CTLA-4) was the first, demonstrating overall survival improvement in metastatic melanoma in the MDX010-20 trial (2010). It extended median OS from 6.4 to 10.1 months — the first treatment to improve survival in advanced melanoma.
