Histone deacetylase 6 and programmed death ligand-1 expressions after neoadjuvant chemotherapy are upregulated in patients with ovarian high-grade serous carcinoma

Patients with ovarian high-grade serous carcinoma (OHGSC) gradually acquire resistance to standard chemotherapy following recurrence. In our previous study on OHGSC, histone deacetylase (HDAC) 6 upregulation led to a poor prognosis, and programmed death ligand-1 (PD-L1) expression was positively correlated with HDAC6 expression. We analyzed HDAC6 and PD-L1 expression before and after chemotherapy to investigate their association with chemotherapy resistance and patient survival. PD-L1 and HDAC6 expression were immunohistochemically analyzed using clinical samples from 54 patients with OHGSC before and after standard chemotherapy. High PD-L1 expression (≥ 5%) was detected in five and nine patients before and after chemotherapy, respectively. The mean PD-L1-positive rate after chemotherapy was 3.88%, which was significantly higher than the rate before chemotherapy (0.68%). The high HDAC6 expression frequency significantly increased from four patients before chemotherapy to 13 patients after. High PD-L1 expression after chemotherapy was significantly correlated with a chemotherapy response score of three, signifying a good chemo-response. High PD-L1 expression after chemotherapy was associated with poor progression-free survival and overall survival in patients who underwent complete surgical resection. In OHGSC, residual tumors after chemotherapy show enhanced HDAC6 and PD-L1 expression. Upregulated PD-L1 after neoadjuvant chemotherapy (NAC) has contradictory characteristics, indicating a good response to chemotherapy but unfavorable survival. It is a wolf in sheep's clothing, and physicians should not make an optimistic prognosis even if the patient shows a good response to NAC. HDAC6 and PD-L1 may be therapeutic targets and prognostic factors for residual tumors after chemotherapy in OHGSC.