Intratumoral heterogeneity in programmed death-ligand 1 immunoreactivity is associated with variation in non-small cell lung carcinoma histotype

Aims Accurate assessment of programmed death-ligand 1 (PD-L1) levels in non-small cell lung carcinoma (NSCLC) samples is complicated by intratumoral heterogeneity. We aimed to: (i) establish whether intratumoral PD-L1 variation is associated with differences in local histotype; (ii) identify histotypes associated with a tendency for there to be higher or lower PD-L1 scores; and (iii) estimate the frequency of clinically significant discordance in PD-L1 levels between intratumoral histotype areas. Methods and results We reviewed 166 NSCLC resection specimens clinically tested for PD-L1 with the 22C3 pharmDx assay. Multiple histotypes were present in 55% (68/123) of non-mucinous adenocarcinoma samples. Solid histotypes had significantly higher PD-L1 levels than other histotypes, both when samples were grouped by predominant histotype, and when histotype areas within a tumour were compared (P < 0.02). Lepidic areas had significantly lower PD-L1 levels than other histotype areas within the same tumour (P < 0.02). Discordance between intratumoral histotype areas at a clinically relevant threshold (PD-L1 tumour proportion score of 1% or 50%) was present in 32% (22/68) of non-mucinous adenocarcinoma specimens with multiple histotype areas. The lepidic histotype was most frequently involved in discordance. Conclusions Intratumoral heterogeneity in PD-L1 is associated with variation in histotype. Over-representation of solid areas may increase the PD-L1 score assigned to a tumour, whereas over-representation of lepidic areas may decrease the PD-L1 score. Evaluation of how histotype representation impacts on the predictive value of PD-L1 testing is warranted.