A Trial of Tigilanol Tiglate in Combination With Pembrolizumab in Stage IIIB to IV M1c-melanoma

Intratumoural treatment with tigilanol tiglate combined with systemic anti-programmed cell death receptor 1 (PD 1) immunotherapy may enhance anti-tumour immune responses and improve outcomes for patients with melanoma. Primary Objectives: 1\. To determine the maximum tolerated dose (MTD) or maximum feasible dose (MFD) level of a single intratumoural treatment of tigilanol tiglate (Tx1) administered in combination with pembrolizumab. 2\. To assess the safety and tolerability of: i) A single treatment (Tx1) of intratumoural tigilanol tiglate at escalating dose levels (dose-escalation) administered in combination with intravenous (IV) pembrolizumab (200 mg); and ii) Repeat treatments of intratumoural tigilanol tiglate (maximum of 3 treatments) administered in combination with IV pembrolizumab (200 mg, Q3W). Repeat treatment(s) of intratumoural tigilanol tiglate to be administered at the same dose level at Tx1 as follows: 1. If the initially injected tumour(s) are not fully ablated, then intratumoural tigilanol tiglate Tx2 +/- Tx3 may be re-administered to the same tumour(s). 2. If the initially injected tumour(s) are fully ablated and additional pre-identified tumours can be treated, then intratumoural tigilanol tiglate, Tx2 +/- Tx3 may also be administered to those tumours. Note: Tumours identified at Screening that are designated as "not to be injected" tumours (i.e. non-injected tumours for observation) cannot be treated at Tx1, Tx2 or Tx3. Secondary Objectives: 1. To evaluate tumour response according to RECIST 1.1 criteria, including loco-regional control of injected tumour(s) and non-injected tumour(s), and survival in patients treated in this study. 2. To assess the safety and tolerability of ongoing treatment with pembrolizumab up to a total of 35 cycles (Q3W), including the combination with up to 3 treatments of intratumoural tigilanol tiglate (Q3W). Exploratory Objectives: 1\. To evaluate the tumour response of tumours following treatment with intratumoural injection with tigilanol tiglate in combination with pembrolizumab