@article {Baldellie002179, author = {Elisa Baldelli and K Alex Hodge and Guido Bellezza and Neil J Shah and Guido Gambara and Angelo Sidoni and Martina Mandarano and Chamodya Ruhunusiri and Bryant Dunetz and Maysa Abu-Khalaf and Julia Wulfkuhle and Rosa I Gallagher and Lance Liotta and Johann de Bono and Niven Mehra and Ruth Riisnaes and Antonella Ravaggi and Franco Odicino and Maria Isabella Sereni and Matthew Blackburn and Angela Zupa and Giuseppina Improta and Perry Demsko and Lucio Crino{\textquoteright} and Vienna Ludovini and Giuseppe Giaccone and Emanuel F Petricoin and Mariaelena Pierobon}, title = {PD-L1 quantification across tumor types using the reverse phase protein microarray: implications for precision medicine}, volume = {9}, number = {10}, elocation-id = {e002179}, year = {2021}, doi = {10.1136/jitc-2020-002179}, publisher = {BMJ Specialist Journals}, abstract = {Background Anti-programmed cell death protein 1 and programmed cell death ligand 1 (PD-L1) agents are broadly used in first-line and second-line treatment across different tumor types. While immunohistochemistry-based assays are routinely used to assess PD-L1 expression, their clinical utility remains controversial due to the partial predictive value and lack of standardized cut-offs across antibody clones. Using a high throughput immunoassay, the reverse phase protein microarray (RPPA), coupled with a fluorescence-based detection system, this study compared the performance of six anti-PD-L1 antibody clones on 666 tumor samples.Methods PD-L1 expression was measured using five antibody clones (22C3, 28{\textendash}8, CAL10, E1L3N and SP142) and the therapeutic antibody atezolizumab on 222 lung, 71 ovarian, 52 prostate and 267 breast cancers, and 54 metastatic lesions. To capture clinically relevant variables, our cohort included frozen and formalin-fixed paraffin-embedded samples, surgical specimens and core needle biopsies. Pure tumor epithelia were isolated using laser capture microdissection from 602 samples. Correlation coefficients were calculated to assess concordance between antibody clones. For two independent cohorts of patients with lung cancer treated with nivolumab, RPPA-based PD-L1 measurements were examined along with response to treatment.Results Median-center PD-L1 dynamic ranged from 0.01 to 39.37 across antibody clones. Correlation coefficients between the six antibody clones were heterogeneous (range: -0.48 to 0.95) and below 0.50 in 61\% of the comparisons. In nivolumab-treated patients, RPPA-based measurement identified a subgroup of tumors, where low PD-L1 expression equated to lack of response.Conclusions Continuous RPPA-based measurements capture a broad dynamic range of PD-L1 expression in human specimens and heterogeneous concordance levels between antibody clones. This high throughput immunoassay can potentially identify subgroups of tumors in which low expression of PD-L1 equates to lack of response to treatment.Data are available upon reasonable request.}, URL = {https://jitc.bmj.com/content/9/10/e002179}, eprint = {https://jitc.bmj.com/content/9/10/e002179.full.pdf}, journal = {Journal for ImmunoTherapy of Cancer} }