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Initial findings from the first reported phase I study looking at nivolumab across multiple tumor types seemed to indicate that PD-1 inhibitors were only effective in PD-L1-positive patients; however, long-term follow-up and data from other trials demonstrated responses in patients with PD-L1-negative disease, Brian I. Rini, MD, notes.
While patients with PD-L1-negative cancer still respond to therapy, it appears that PD-L1-positive patients respond better, Rini notes. However, in studies looking at the combination of the CTLA-4 inhibitor ipilimumab and nivolumab the responses were the same, regardless of PD-L1 expression. As a result, it remains unanswered whether PD-L1 will serve as an effective biomarker in this space.
A variety of definitions and methods for PD-L1 have added to the confusion, Rini notes. Another obstacle to overcome is the definition itself of PD-L1-positivity. At this point, substantial research is still required to fully understand PD-L1 as a biomarker of response.