Trial Subjects (patients) who are deemed eligible for the trial will initially be entered into the safety run-in stage of the trial. Up to 12 patients will be registered into the safety run-in stage, in cohorts of 3 patients at a time.~3 patients will be registered initially and will be administered a single infusion of pembrolizumab (200mg, day 1) in combination with CXD101 (20mg twice daily days 1 to 5). This is dose level 0.~If 0 to 1 dose limiting toxicity (DLT) is observed, 3 more patients will be entered into the trial and treated at dose level 0. If 0 to 1 DLT is observed across all 6 patients, the maximum tolerated dose (MTD) will be declared and the expansion stage of the trial will be opened.~If more than 1 DLT is observed at dose level 0, 3 patients will be recruited and treated at dose level -1. The CXD101 dose will be reduced by 25% (20mg in the morning and 10mg in the evening, days 1 to 5), while the pembrolizumab dose will remain the same (200mg, day 1).~If 0 or 1 DLT is observed, 3 more patients will be recruited and treated at dose level -1. If 0 or 1 DLT is observed across all 6 patients the maximum tolerated dose will be declared and the expansion stage of the trial will be opened.~If more than 1 DLT is observed at dose level -1 the combination will be deemed excessively toxic and no further patients enrolled.~Once the MTD is declared, the cohort will be expanded and a further 33 patients will be treated at this dose level.~Patients will continue to receive pembrolizumab and CXD101 at 3 weekly intervals for a maximum of 2 years or until disease progression or unacceptable toxicity develops. Patients on pembrolizumab will be seen every 3 weeks during trial treatment. Patients who progress will be seen annually for disease status. Patients completing treating or who stop treatment early for reasons other than disease progression will be followed every 3 months for up to one year after the end of treatment, and annually thereafter until end of trial is declared (when the last patient has completed 1 year follow up).
Trial Subjects (patients), will receive single infusions of pembrolizumab in combination with CXD101 every 3 weeks for two years or until disease progression or unacceptable toxicity develops.