With the approval of various PD-1/PD-L1 immune checkpoint inhibitors for advanced NSCLC, a new class of predictive biomarker assays – complementary and companion diagnostics – has emerged.17 Yet, these assays have often differed in many respects across anti-PD-1/PD-L1 trials and treatments (e.g. distinct staining properties and sensitivities).18 Such distinctions and potential lack of compatibility across treatments could prevent their interchangeability in clinical use. The gene discussed is PDCD1; the disease is non-small cell lung carcinoma.