Additionally, they found that low density of PD-1 and PD-L1 expressing cells in tumor tissue was significantly associated with advanced disease, failing to show any significant association between survival and PD-1 or PD-L1 expression in ovarian cancer (17), while patients with recurrent tumors and increased infiltrating PD-1+ immune cells had longer OS (21). This evidence concerns the gene PDCD1 and ovarian cancer.