Julia Pagliuso, Suzanne Parry, Zenobia Haffajee, Tony Badrick, Keith Miller Background . One important initiative that commenced at the Royal College of Pathologists of Australasia Quality Assurance Program (RCPAQAP) in 2017 was the collaboration with United Kingdom National External Quality Assessment Scheme (UK NEQAS) Immunocytochemistry (ICC) and In-Situ Hybridization (ISH) for the challenging implementation of a PD-L1 immunohistochemistry (IHC) proficiency testing program for non-small cell lung carcinoma (NSCLC). A RCPAQAP participant survey in 2016 showed that only eight laboratories were performing PD-L1 testing. The aim of the collaboration was to increase the sample size of the pilot program to provide meaningful results that could be reported back to RCPAQAP participants with appropriate recommendations. Other challenges of assessment included standardising the clinical cut-offs for positivity for each commercial assay, interpretation of laboratory developed tests (LDTs), using appropriate tissue to cover the critical interpretation points for each assay, interchangeability of clones and interpretation proficiency testing. Methods . The use of a ‘Gold Standard’ for each commercial assay was used as a baseline to compare participant results and tumour proportion score bin categories were implemented to harmonise interpretation across clones. Conclusions . The findings of the pre-pilot test suggest that the use of a clinically validated PD-L1 IHC assay performs better during assessment than adopting a laboratory developed test (LDT). The assessment committee also concluded that tonsil showed a better dynamic range of positivity than placenta. It was acknowledged that participants are limited by the platforms they have available and so it was suggested that validating an optimal method against the clinical assay and continual verification of the test may produce the expected result. The next big challenge is to extend proficiency testing from technical to interpretation. This is being implemented globally via the International Quality Network for Pathology (IQNPath) with participation through local External Quality Assurance programs, including RCPAQAP.