PTGER1 and metastatic malignant neoplasm in the lymph nodes: However, in the subgroup of patients with lymph-node metastasis, patients with enhanced EP1 expression (IRS > 3) showed significantly worse overall survival than patients with low EP1 expression (IRS ≤ 3) (median estimate: 2.6 years vs. 8.6 years; p = 0.028) (Fig. 2).