Objective Low-grade serous ovarian cancers (LGSOC) characterize less frequent incidence of lymph-nodes (LN) metastasis. Ki67 expression level is associated with prognosis and therapy outcome differences. Its’ expression in combination with lympho-vascular space invasion (LVSI) have not been evaluated in prediction of LN involvement yet.

Methods Patients with LGSOC were identified in institutional database. Receiver-operator characteristics (ROC) curve analysis was performed to find cut off values of Ki67% to discriminate patients with LN metastasis. The association between LVSI presence and LN involvement was performed.

Results A total of 109 patients treated between 2000 and 2018 with primary LGSOC were identified in our institution database. Complete data of Ki67 expression and LVSI in patients who underwent lymph node dissection was obtained in 61 (84.7%) of those patients. Presence of LVSI was associated with higher risk of lymph-nodes metastases in univariate und multivariate analysis (p < 0.001 and p = 0.01 respectively). Ki67≥6% was associated with higher risk of LVSI presence (p = 0.017). No significant correlation between Ki67 expression level and nodal metastases was found (p = 0.145). Neither presence of LVSI, nor nodal metastases were associated with prognosis differences.

Conclusions It is the first study showing association between LVSI presence, Ki67 expression and risk of lymph-node metastasis in primary low-grade ovarian cancer. Further prospective trials evaluating LVSI and Ki-67 as a predictor of lymph-node metastasis should be planned.