Introduction: Positive surgical margin (PSM) on radical prostatectomy (RP) is associated with an increased risk of biochemical recurrence and use of salvage therapies. Given these adverse consequences, exploration of time trends and predictors of PSM will improve the patient outcomes following surgery for prostate cancer. Methods: Pathological data from RP patients treated from 2011-2020 was extracted from the Victorian Prostate Cancer Outcomes Registry. This is a clinical quality registry that regularly benchmarks and reports back to individual clinicians the PSM percentage for their patients. Trends in PSM over time were visualised with separate running mean plots for both pT2 and pT3/4 disease. Predictors of PSM were explored with multivariable regression with date of surgery, surgical method, and hospital type, public or private, entered as covariates. Results: In total, 12394 patients formed the sample with PSM recorded in 25% (n=3141) of patients, 12% (777/6640) in pT2 disease and 41% (2364/5754) in pT3/4 disease. Comparing 2011-12 to 2019-20, the pT3/4 PSM proportion declined from 50% to 38% while pT2 percentages were steady at 13%. In "high volume" institutions, pT2 PSM fell from 12% to 6.5%. Independent predictors of lower PSM were robotic vs open method and being treated at a private vs public institution. Conclusions: A clear decline in the proportion of pT3 PSM was observed in a large prostate cancer registry. Proposed explanatory factors include improved technical proficiency with robotic surgery and participation in a registry-based quality improvement initiative. SOURCE OF Funding: The Victorian Prostate Cancer Outcomes Registry is supported by Movember. Marlon Perera is sponsored by the Australian-America Fulbright Commission administered through a 2021-2022 Fulbright Future Scholarship funded by The Kinghorn Foundation. MSKCC is supported by NIH/NCI Cancer Center Support Grant to Memorial Sloan Kettering Cancer Center (P30 CA008748).
