Abstract Introduction/Objective Introduction: In contrast to traditional labs, our CAP/CLIA Lab performs patient sample testing only for pharma-sponsored clinical trials. Very limited patient material is received, usually in the form of unstained slides rather than wet tissues. Strict run control (RC) quality measures are therefore essential to avoid repeat testing, exhaustion of patient material and/or delay of patient enrollment decisions. We describe methods to optimize RC staining performance and consistency. Methods/Case Report Methods: The RC failure rate was evaluated retrospectively and prospectively from January 2018 through March 2021. Specific failure modes were evaluated, including: 1) instrument-related (catastrophic mechanical failure, slide derailment, low temperature error), 2) stain-related (lighter or darker staining vs. reference), 3) tissue-related (tissue loss/fall-off). RC failures were also tracked by instrument and by individual biomarker. Results (if a Case Study enter NA) Results: 33,189 patient samples (84,130 slides) were tested from January 2018 through March 2021. Concurrently, 14,794 RC slides were tested across more than 115 biomarkers, including immunohistochemistry, multiplex immunofluorescence, and in situ hybridization assays. The RC failure rates by year were: 2018: 3.2 % (116 RCs), 2019: 3.8% (156 RCs), 2020: 1.9% (100 RCs), and 2021 (through March) 1.3% (21 RCs). The decrease in RC failure rate was a direct result of process changes addressing each of the failure modes, including, but not limited to: 1) improvement in slide storage conditions, 2) more selective RC tissue selection, and 3) more consistent interaction with on-site instrument support. Conclusion Process improvements addressing pre-analytic and analytic RC failure modes have resulted in a year-over-year decrease in RC failures. Consequently, our first-pass rates for immunohistochemical, immunofluorescence multiplex, and in-situ hybridization testing of patient samples have increased. Close monitoring of RC failure rates and near-real-time troubleshooting of individual RC failures are important components of successful operation in our unique laboratory setting, where patient material for testing is limited.