Background: Programmed death-ligand 1 (PD-L1) expression determines the eligibility for anti-PD-1 treatment in patients with advanced gastric cancer, but evidence indicates that PD-L1 staining is heterogeneous. Patients who are ineligible for radical surgery could be tested for PD-L1 expression with biopsy staining, but it is unclear if a small biopsy is representative of the PD-L1 status of the whole tumor. The aim of our study was to determine how many biopsy specimens are needed to accurately reflect the objective status of PD-L1 expression in whole sections. Methods: We built tissue microarrays (TMAs) as substitutes for core biopsies, collecting 6 cores per case from 152 gastric cancer specimens. All of the slides and TMAs underwent PD-L1 immunohistochemical staining, and PD-L1 expression in at least 1% of tumor cells or immune cells was defined as positive. Results: It was necessary to randomly select multiple cores from TMAs to reach a suitable agreement rate (> 90%) and Cohen’s κ value (> 0.8) between TMAs and whole sections. We defined the PD-L1 staining status from the whole section as the standard. The evaluation of five randomly selected cores from TMAs agreed well with the evaluation of whole sections. The sensitivity, specificity and the area under the curve (AUC) of the receiver-operating characteristic (ROC) were 0.93, 0.92, and 0.922 (95% confidence interval (CI) 0.863–0.982), respectively. Conclusions: We conclude that PD-L1 expression among TMA samples had different degrees of relevance to the corresponding surgical specimens, which indicates that at least five biopsies might be necessary to characterize patients taking anti-PD-1 treatment.

Metastatic colorectal cancer (mCRC) is a major cause of death of malignant tumor and the valuable prognostic biomarker for chemotherapy is crucial in decreasing mortality. Previous studies have proved the prognostic value of the mean platelet volume (MPV) in survival of primary operable CRC patients. However, the prognostic impact of MPV in mCRC is still unclear. In this study, we aimed to clarify the prognostic role of MPV in mCRC undergoing standard first-line chemotherapy. From January 2012 to December 2016, we conducted a retrospective clinical study included 264 mCRC patients (NCT03532711). All the enrolled patients received the standard oxaliplatin-based or irinotecan-based chemotherapy. The association between the baseline MPV and clinicopathological features were examined. Univariate analysis revealed that decreased MPV, the platelet counts (PLT), platelet-to-lymphocyte ratio (PLR) and the platelet crit (PCT) were significantly associated with inferior overall survival (OS) (p < 0.05). On multivariate analysis, elevated PLR was significant prognostic factors for OS, with hazard ratios of (HR:1.006, 95% CI:1.001–1.011, p = 0.01) while MPV was not, respectively (p < 0.05). Our study demonstrated that the baseline MPV level may act as a predictive factor for survival in mCRC patients undergoing standard chemotherapy. This study was retrospectively registered in date May the 20th 2018. The registration number (TRN) of this study was NCT03532711 .