In October 2016, the FDA announced that pembrolizumab (KEYTRUDA®) is was approved for the first-line treatment of metastatic NSCLC patients whose tumors express high levels of PD-L1 (Tumor Proportion Score [TPS] of ≥50%) or for previously treated metastatic NSCLC patients whose tumors express PD-L1 (TPS of ≥1%). PD-L1 expression levels are determined using the 22C3 PharmDx assay. Prior to this, chemotherapy was the standard first-line treatment for most NSCLC patients. Pembrolizumab was the second FDA-approved PD-1 inhibitor in lung cancer, and first across all NSCLC histologies. The PD-1 agent nivolumab (Opdivo®) was approved in March 2015 for patients with NSCLC who have progressed on or after platinum-based chemotherapy. However, the indication is limited to individuals with squamous histology.
A total of ~6000 patients were screened for eligibility in clinical trials KEYNOTE-001, KEYNOTE-010, and KEYNOTE-024. This is one of the largest data sets of PD-L1 expression determined by an FDA-approved companion diagnostic in patients with advanced NSCLC screened for pembrolizumab therapy. 68% of patients with advanced NSCLC had PD-L1 TPS ≥1% and 28% had PD-L1 TPS ≥50%. The prevalence is similar across prior lines of therapy and different disease characteristics examined.
Acceptable specimens for the assay are formalin (10% buffered or Zinc formalin)-fixed (6-48 hours), paraffin-embedded NSCLC tissue specimens. Sectioned slides must be analysed within 3 months after sectioning date.
In archival tissue of > 6 months old the PD-L1 protein can be deteriorated resulting in unreliable staining.
One representative paraffin block is preferred. Alternatively, 3 unstained freshly sectioned tissue sections are accepted (1 slide of 4 or 5 µm thickness for H&E staining and a minimum of 2 slides of 4-5 µm thickness for PDL1 IHC testing).
Maintain and ship specimens at ambient temperature.
Fixatives other than buffered formalin, prolonged fixation time, decalcification methods, or exposure to severe heat or chemicals may give rise to inadequate results.
Three to five business days for slides and paraffin blocks respectively.