A Phase I, Open-Label Study of GSK3174998 Administered Alone and in Combination With Anticancer Agents Including Pembrolizumab in Subjects With Selected Advanced Solid Tumors

This is a first time in human (FTIH), open-label, non-randomized, multicenter study designed
to evaluate the safety, tolerability, pharmacokinetics (PK), pharmacodynamics, and
preliminary clinical activity of GSK3174998 administered intravenously to participants with
selected advanced or recurrent solid tumors. This dose-escalation study will assess the
safety, activity of GSK3174998 as monotherapy (Part 1), in combination with pembrolizumab
(Part 2), and potentially in combination with additional therapies.

The study will be conducted in 2 parts, each part consisting of starting with a
dose-escalation phase followed by a cohort expansion phase. GSK3174998 will first be
evaluated as monotherapy in escalating doses. Once a dose of GSK3174998 has been identified
that is both tolerable and demonstrates pharmacodynamic activity, enrollment of Part 2 may
begin. In Part 2, escalating doses of GSK3174998 will be evaluated with fixed doses of
pembrolizumab.

The maximum duration of treatment with GSK3174998 and pembrolizumab will be approximately 2
years or 35 cycles, whichever comes first. The follow-up period for safety assessments will
be a minimum of 3 months from the date of the last dose. The post-treatment follow-up period
will include disease assessments every 12 weeks until documented progressive disease (PD).
Approximately 141 participants with selected advanced or recurrent solid tumors will be
enrolled.