We confirmed in a cohort of advanced stage serous ovarian cancers that patients with high K5/6 or high K5 immunostaining (≥ 10.0%) had a significantly reduced PFS compared to patients with low K5/6 or low K5 positivity (< 10.0%, Figure 4A, 4C). The 24 months PFS rate was 34.4% in the group of patients with K5/6 positivity < 10% and only 10.5% in the group of patients with K5/6 positivity ≥ 10%. The 24 months PFS rate was 48.5% in the group of patients with K5 positivity < 10% and only 27.7% in the group of patients with K5 positivity ≥ 10%. Neither K5/6 nor K5 immunostaining was associated with OS (Figure 4B, 4D). Cox regression analysis also indicated that patients with high K5/6 positivity (≥ 10%) had a 1.78 fold increased risk of disease relapse (95% CI; 1.01–2.66, P = 0.017, Table 2). High K5 positivity was associated with a 1.90 fold increased risk of disease relapse (95% CI; 1.12–3.19, P = 0.017, Table 2). Other clinical and pathological parameters including patient age, clinical stage, tumor grade, and the presence of residual disease were not associated with PFS or OS in this advanced stage serous ovarian cancer cohort (Table 2).