Preoperative staging using magnetic resonance imaging and risk of positive surgical margins after prostate-cancer surgery.
BACKGROUND: It is unclear whether preoperative staging using Magnetic Resonance Imaging (MRI) reduces the risk of positive margins in prostate cancer. We aimed to assess the effect on surgical margins and degree of nerve sparing of a pelvic MRI presented at a preoperative MRI conference. METHODS: Single institution, observational cohort study including 1037 men that underwent robot assisted radical prostatectomy between October 2013 and June 2015. Of these, 557 underwent a preoperative MRI combined with a preoperative MRI conference and 410 did not. With whole-mount prostate specimen histopathology as gold standard we assessed the ability of MRI in finding the index tumor and the sensitivity and specificity for extra prostatic extension. We calculated relative risks for positive surgical margins and non-nerve sparing procedure, adjusting for preoperative risk factors using stabilized inverse-probability weighting. RESULTS: MRI detected the index tumor in 80% of the cases. Non-organ confined disease (pT3) at histology was present in the MRI and the non-MRI group in 42% and 24%, respectively. Rate of positive surgical margins comparing the MRI and non-MRI groups was 26.7% and 33.7%, respectively, relative risk 0.79 [95% CI 0.65-0.96], weighted relative risk (wRR) 0.69 [95% CI 0.55-0.86]. The wRR of extensive positive surgical margins was 0.45 [95% CI 0.31-0.67]. Undergoing MRI was also associated with an increased risk of being operated with a non-nerve sparing technique (wRR, 1.84 [95% CI 1.11-3.03]). CONCLUSIONS: Our study suggests that preoperative prostate MRI in combination with a preoperative MRI conference affects the degree of nerve-sparing surgery and reduces positive surgical margins.