The first studied applied to NSCLC did not show significant difference between the primary and the metastatic sites. Initial recommendations were to utilize what is available. New studies in other types of cancer and especially triple negative breast cancers show higher PDL1 positivity in the primary site compared to the metastatic sites.

Depends on the underlying algorithm TPS vs CPS. TPS is for the time being only used for the 3D application (Pembrolizumab-NSCLC-22C3 PDL1 assay) and relies on TPS which is the percentage of tumoural cells expressing PDL1. For all other 3D applications (and possibly for all future ones) CPS is performed. CPS is not a percentage but a score which is a fraction from 0 to 100. If the fraction is greater than 100, the score is reported as 100. The numerator includes the number of PDL1 positive immune cells + the number of PDL1 positive tumoural cells; the denominator includes the total number of tumoural cells (positive and negative). In order to be accepted as a positive immune cell, that immune cell has to be in the tumoural bed. Therefore only biopsy and surgical specimens can guarantee the tissue integrity and the relationship of immune cells with the tumoural bed.