Examining the evidence for immune checkpoint therapy in high-grade serous ovarian cancer

The 5-year survival rate for ovarian cancer has remained relatively static over the past number of years, which can be attributed in part to the lack of new therapeutic strategies to target this disease. Although numerous other cancer types have benefited from the success of immune checkpoint inhibitors, their use in clinical trials targeting ovarian cancer has shown limited efficacy. Most clinical trials have focused on PD-1/PD-L1 immune checkpoint blockade, either as a monotherapy or in combination with chemotherapies, however inhibiting other pathways may potentially be more efficacious in treating ovarian cancer. For example, drugs targeting some emerging immune checkpoints (such as LAG-3, TIM-3, TIGIT and PVRIG), are entering into clinical trials, which could show improved success for ovarian cancer patients. Similarly, predictive biomarkers that have been approved for use with immune checkpoint inhibitors, such as PD-L1 expression, are limited, as only the presence or absence of PD-L1 is assessed. However, the development of next generation predictive biomarkers, which assesses density and location of tumour infiltrating lymphocytes, could be more beneficial for this heterogenous cancer. In this review we discuss the use of immune checkpoint inhibitors in ovarian cancer, with a focus on high-grade serous disease, and delve into what the future may hold for immunotherapy in this cancer type.