Introduction/Background HIPEC improves overall survival in patients with stage III epithelial ovarian cancer after neoadjuvant therapy compared to interval cytoreductive surgery (CRS) alone. The immediate impact of HIPEC on the systemic immune response has not been well characterised. We sought to document the impact of cisplatin-based HIPEC on the systemic immune response.

Methodology Longitudinal analysis of neutrophil to lymphocyte ratio (NLR) and monocyte to neutrophil ratio (MLR) results in 22 age and stage matched patients with stage IIIc EOC were examined. Flow cytometric analysis (FACs) was performed on intra-operative PBMCs before and after HIPEC in 3 patients. Independent sample t test and one way ANOVA was used to analyse results using SPPS version 24.

Results 9 patients had primary CRS, 8 had interval CRS+ cisplatin HPEC (50 mg/m² at 40°C for 60 min), and 5 had interval CRS with no HIPEC. All patients had aggressive CRS and an CC0 resection. The interval CRS (no HIPEC) group had a significantly lower day 1 NLR compared to interval CRS HIPEC group (p=0.047). The NLR of all groups was similar by day 4. The MLR in the three groups was similar at all time points. FACs of peripheral CD3⁺ T Cells demonstrated that HIPEC increased circulating CD8⁺ T Cells and reduced expression of the immune checkpoint protein TIGIT (p<0.05).

Conclusion Cisplatin-based HIPEC causes an rapid and short-lived change in the systemic immune response. Our initial findings that HIPEC alters the expression of immune checkpoint proteins on CD8⁺ T cells suggests that further investigations of the combination of HIPEC and immunotherapy may be warranted.

Disclosure Nothing to disclose.