Background Mucinous and serous borderline ovarian tumours (mBOTs and sBOTs) are controversial diseases.Objectives With this systematic review we aim to evaluate the different high-risk histopathological features and recurrence rates. Data collection and analysis Lethal recurrence data for micropapillary patterns (MPs), microinvasion, non-invasive and invasive implants, and intraepithelial carcinoma (IECA). The primary measure of effect was the odds ratio of lethal recurrence reduction.Results Data from patients in 42 studies including 4414 sBOTs and 12 studies including 894 mBOTs were pooled. Of these, 53.3% presented early-stage typical sBOTs, 24.4% presented with MPs, 22.3% presented with microinvasion, 34.4% presented with non-invasive implants, and 7.3% presented with invasive implants. The pooled lethal recurrence rates were, respectively: 18.3, 16.8, 10.7, 16.2, and 33.8%. Patients with MPs were more likely to suffer lethal recurrence when compared with high-stage sBOTs (odds ratio, OR 0.501; P = 0.003), whereas the trend in microinvasive sBOTs did not reach statistical significance. Regarding mBOTs, 61.6% presented with early-stage typical mBOTs, 19.6% presented with microinvasion, 34.8% presented with IECA, and six patients presented with non-invasive implants; none presented with invasive implants. The lethal recurrence rates were, respectively: 3.6, 0, 3.7, and 0%.Conclusion Micropapillary patterns (MPs) showed a higher risk for lethal recurrence when compared with high-stage sBOTs. Regarding mBOTs, IECA and microinvasion do not play a role in the lethal recurrence rate.Keywords Intraepithelial carcinoma, invasive implants, microinvasive borderline ovarian tumours, micropapillary serous borderline ovarian tumours, mucinous borderline ovarian tumours, non-invasive implants.Tweetable abstract Micropapillary pattern confirmed as high-risk in BOT. IECA and microinvasion don't play a role in mucinous BOT.
