In a highly anticipated presentation at the European Society for Medical Oncology (ESMO) 2017 Congress in Madrid, Spain, Incyte unveiled updated data from the ongoing Phase I/II KEYNOTE-037/ECHO-202 trial. The study is evaluating Incyte’s selective IDO1 enzyme inhibitor epacadostat in combination with Merck & Co.’s anti-PD-1 Keytruda (pembrolizumab) in patients with advanced melanoma.

The analysis was focused on the ‘efficacy evaluable’ cohort of patients with advanced melanoma that were treated with the combination (N=63). The majority of this population had not received prior systemic treatment for advanced disease (N=53). Epacadostat (25mg, 50mg, and 100mg) was investigated in combination with Keytruda at 2mg/kg or 200mg fixed dose every three weeks.

The promising clinical activity of Keytruda + epacadostat was re-affirmed, with 56% of patients treated with the combination responding to therapy. In addition, 30/35 responses were ongoing at data cut-off. Partnering these two agents remarkably withheld disease progression for a median progression-free survival (PFS) of 12.4 months. Results were consistent across dosing schedules of epacadostat combined with Keytruda (including epacadostat 100mg twice daily, the dose used in the pivotal Phase III KEYNOTE-252/ECHO-301 trial) and were evident regardless of PD-L1 and BRAF mutation status.

The data has increased the expectations of immuno-oncology watchers and shown that initiation of the much larger Phase III KEYNOTE-252/ECHO-301 trial, which has accrued more than 600 patients, is warranted.

Efficacy comparisons are inevitably drawn with marketed PD-1 monotherapies Keytruda and Opdivo (nivolumab), as well as with BMS’ combination strategy of PD-1 with Yervoy (ipilimumab), a cytotoxic T-lymphocyte-associated protein 4 (anti-CTLA-4) inhibitor. Cross-trial comparative data used for illustrative purposes indicated the potential of Keytruda + epacadostat to achieve superior median PFS to reported median PFS values for the currently approved regimens, with 11.5 months for Opdivo + Yervoy and 6.9 months for Opdivo monotherapy in CheckMate 067 (Bristol-Myers Squibb, NCT01844505); and 5.6 months for Keytruda every two weeks and 4.1 months for Keytruda every three weeks in KEYNOTE-006 (Merck & Co, NCT01866319).

From a safety perspective, Keytruda + epacadostat appears to have very mild toxicities with no increase in Grade 3/4 treatment-related adverse events in comparison with Keytruda monotherapy, with the exception of rashes. This could prove an incisive differentiating factor against Opdivo + Yervoy, which is marred by considerable serious toxicities.

Results from the Phase III KEYNOTE-252/ECHO-301 trial are eagerly anticipated. However, early signals from the Phase I/II KEYNOTE-037/ECHO-202 trial indicate that the doublet has a great chance to stand out from existing regimens and that its success may be practice-changing in the frontline setting of advanced melanoma.