biostudies-literatureGiraldo NABloomberg~Kimmel Institute for Cancer Immunotherapy, Sidney Kimmel Comprehensive Cancer Center, Johns Hopkins UniversityBristol-Myers SquibbStand Up To Cancer–Cancer Research Institute Cancer Immunology Translational Cancer Research GrantCancer Immunotherapy Trials NetworkMelanoma Research AllianceNational Cancer InstituteNCI NIH HHSNational Institutes of HealthSidney Kimmel Comprehensive Cancer Center99https://www.ebi.ac.uk/biostudies/studies/S-EPMC6167897biostudies-literatureUnknown6(1)<h4>Background</h4>We recently reported a 56% objective response rate in patients with advanced Merkel cell carcinoma (MCC) receiving pembrolizumab. However, a biomarker predicting clinical response was not identified.<h4>Methods</h4>Pretreatment FFPE tumor specimens (n = 26) were stained for CD8, PD-L1, and PD-1 by immunohistochemistry/immunofluorescence (IHC/IF), and the density and distribution of positive cells was quantified to determine the associations with anti-PD-1 response. Multiplex IF was used to test a separate cohort of MCC archival specimens (n = 16), to identify cell types expressing PD-1.<h4>Results</h4>Tumors from patients who responded to anti-PD-1 showed higher densities of PD-1+ and PD-L1+ cells when compared to non-responders (median cells/mm², 70.7 vs. 6.7Journal for immunotherapy of cancerMultidimensional, quantitative assessment of PD-1/PD-L1 expression in patients with Merkel cell carcinoma and association with response to pembrolizumab.PMC6167897SU2C-AACR-DT1012P30 CA006973IH/NCI Cancer Center Support Grant P30 CA015704P30 CA015704UM1 CA154967T32 CA193145K24 CA139052R01 CA142779Anders RACheever MNghiem PTSunshine JCDanilova LKaunitz GJLipson EJFling SBerry SGiraldo NAChurch CDSuccaria FTaube JMLundgren LGreen BOgurtsova ASoni AYearley JHNguyen PXu HEngle ELMiller NJRamchurren NStein JECuda JDCottrell TRTopalian SLfalseMultidimensional, quantitative assessment of PD-1/PD-L1 expression in patients with Merkel cell carcinoma and association with response to pembrolizumab.<h4>Background</h4>We recently reported a 56% objective response rate in patients with advanced Merkel cell carcinoma (MCC) receiving pembrolizumab. However, a biomarker predicting clinical response was not identified.<h4>Methods</h4>Pretreatment FFPE tumor specimens (n = 26) were stained for CD8, PD-L1, and PD-1 by immunohistochemistry/immunofluorescence (IHC/IF), and the density and distribution of positive cells was quantified to determine the associations with anti-PD-1 response. Multiplex IF was used to test a separate cohort of MCC archival specimens (n = 16), to identify cell types expressing PD-1.<h4>Results</h4>Tumors from patients who responded to anti-PD-1 showed higher densities of PD-1+ and PD-L1+ cells when compared to non-responders (median cells/mm², 70.7 vs. 6.72018-01-01T00:00:00Z2018 Oct2025-04-22T12:55:08.892Z2019-03-26T23:59:42ZS-EPMC61678973028585210.1186/s40425-018-0404-0