PD-L1 Expression and Pembrolizumab Use in Advanced Non-Small Cell Lung Cancer
Pembrolizumab use in advanced NSCLC is critically dependent on PD-L1 expression levels, with distinct treatment algorithms based on tumor proportion score (TPS) thresholds of ≥50%, 1-49%, and <1%. 1
First-Line Treatment Algorithm by PD-L1 Expression
PD-L1 TPS ≥50% (High Expression)
For patients with PD-L1 TPS ≥50%, pembrolizumab monotherapy (200 mg IV every 3 weeks) is the preferred first-line option, demonstrating superior survival compared to platinum-based chemotherapy (median PFS 10.3 vs 6.0 months; HR 0.5; OS HR 0.6) 1. This applies to both squamous and non-squamous histologies without EGFR/ALK alterations 1.
However, pembrolizumab plus chemotherapy can be considered in specific high-risk cases even with PD-L1 ≥50%, particularly when:
- High tumor burden requires rapid disease control
- Symptomatic disease necessitates immediate response
- Patient has poor performance status (PS 2) where monotherapy may be insufficient 1
For non-squamous: pembrolizumab + pemetrexed + carboplatin 1 For squamous: pembrolizumab + carboplatin + (nab-)paclitaxel 1
Critical nuance: Patients with PD-L1 expression 90-100% demonstrate significantly better outcomes than those with 50-89% (ORR 60% vs 33%, mPFS 14.5 vs 4.1 months, HR 0.50) 2. This suggests the highest expressors derive maximal benefit from monotherapy.
PD-L1 TPS 1-49% (Intermediate Expression)
For PD-L1 TPS 1-49%, combination pembrolizumab plus chemotherapy is the standard of care 3, 4. Monotherapy pembrolizumab is insufficient in this population.
Recommended regimens:
- Non-squamous: pembrolizumab + pemetrexed + carboplatin (5-year OS 20.6% vs 7.6% with chemotherapy alone; HR 0.61) 3
- Squamous: pembrolizumab + carboplatin + paclitaxel or cemiplimab + carboplatin + paclitaxel 3
Alternative options (may offer):
- Nivolumab + ipilimumab (dual checkpoint inhibition)
- Nivolumab + ipilimumab + 2 cycles platinum chemotherapy (CheckMate 9LA: HR 0.61 for OS) 3
- Durvalumab + tremelimumab + platinum chemotherapy 3
PD-L1 TPS <1% (Negative/Low Expression)
For PD-L1 <1%, pembrolizumab plus chemotherapy remains effective and is recommended 3, 4. The same combination regimens apply as for TPS 1-49%.
Important consideration: Recent meta-analysis data suggest pembrolizumab-chemotherapy combinations improve OS even in PD-L1 <1% patients (HR 0.67), though benefits are less pronounced than in higher expressors 5, 6. The survival benefit persists despite low PD-L1 expression (OS HR 0.60) 7, challenging the notion that PD-L1 negativity precludes immunotherapy benefit.
Second-Line Treatment After Progression
If First-Line Was Chemotherapy (No Prior Immunotherapy)
PD-1/PD-L1 inhibitors are the treatment of choice for second-line therapy 8:
- Nivolumab: recommended regardless of PD-L1 expression (both squamous and non-squamous) 8
- Pembrolizumab: requires PD-L1 TPS ≥1% 8
- Atezolizumab: recommended regardless of PD-L1 expression 8
There is enriched efficacy with higher PD-L1 expression in second-line, but unselected patients still benefit compared to docetaxel 8. In clinical practice, nivolumab or atezolizumab are often preferred over pembrolizumab to avoid requiring PD-L1 testing 1.
If First-Line Was Pembrolizumab
Platinum-based chemotherapy is recommended as second-line treatment after pembrolizumab progression 8, 9, 8. Rechallenge with anti-PD-1 therapy may be considered only if substantial prior clinical benefit was achieved and discontinuation was not due to progression or severe toxicity 4.
Critical Testing and Selection Considerations
PD-L1 testing should be performed at diagnosis using FDA-approved companion diagnostics 1:
- 22C3 pharmDx assay (for pembrolizumab)
- Results reported as tumor proportion score (TPS): percentage of tumor cells with membranous PD-L1 staining
- Testing can be performed on archived or fresh tissue 1
Common pitfalls to avoid:
- Do not use pembrolizumab monotherapy for PD-L1 <50% in first-line—this is inadequate
- Do not withhold pembrolizumab-chemotherapy combinations from PD-L1 <1% patients based solely on biomarker status
- Performance status matters: PS 2 patients can receive immunotherapy but require careful selection 8; PS 3-4 should receive best supportive care only 8, 9
- Corticosteroid exposure and poor ECOG PS negatively impact pembrolizumab outcomes 10
Contraindications requiring chemotherapy alone 4:
- Active autoimmune disease requiring systemic therapy
- Medical conditions requiring immunosuppression
- Never-smokers may have reduced benefit from immunotherapy in second-line 4
Special Populations
Elderly patients (≥65 years): Apply standard recommendations; no dose adjustments needed 8, 9, 8, 11
PS 2 patients: Checkpoint inhibitors can be considered, though data are limited; carboplatin-based doublets preferred if chemotherapy chosen 8