Kulangara et al reported the Combined Positive Score (CPS) for immunostaining of Programmed Death Ligand-1 (PD-L1). A positive score is an indication for pembrolizumab therapy in a patient with gastric cancer. The authors are from Dako North America, Agilent Technologies and Merck Research Laboratories.
Patient selection: gastric cancer
Testing: immunostaining for PD-L1
Adequacy: >= 100 viable tumor cells
Parameters:
(1) total number of viable tumor cells
(2) number of tumor cells show partial or complete membrane staining
(3) number of mononuclear cells (lymphocytes, macrophages) showing any staining
combined positive score =
= MIN(100, ((number of tumor cells staining)+(number of mononuclear cells staining))/(total number of viable tumor cells)*100)
Interpretation:
• minimum score: 0
• maximum score: 100
• A score < 1 indicates negative staining.
• A score >= 1 indicates positive staining.
Limitations:
• The immunostaining procedure must be performed reliably with optimally dilated antibodies.
