PD-L1 Expression as a Predictive Biomarker: Is Absence of Proof the Same as Proof of Absence?

As targeted therapies are superior to standard chemotherapy in select patients, effective predictive biomarkers are needed to identify patients who are more likely to respond to targeted therapies. Using a tumor sample, biomarker testing is often protein- or nucleic acid–based. In cases of non–small-cell lung cancer (NSCLC), tumor cells are tested for epidermal growth factor receptor mutations and anaplastic lymphoma kinase rearrangements, and the results help the oncologist to tailor therapy based on individual tumor genetics.