STAT3 and cancer: Upregulation of PD‐L1 on tumor cells helped to develop well‐known checkpoint inhibitor therapies for cancer and it is widely accepted that PD‐L1 expression in tumor cells is controlled by either interferon receptor signaling[24] or IL6/JAK/STAT3 signaling axes.[25]Here, we found another signaling axis that regulates PD‐L1 expression on tumor cells: S1P upregulates PD‐L1 expression in ovarian cancer cells via the E2F1 transcription factor.