Study BT8009-100 in Subjects With Nectin-4 Expressing Advanced Malignancies

This study will assess the safety and tolerability of BT8009 alone and in combination with pembrolizumab in patients with select advanced solid tumors. BT8009 will be given as a single agent in 3 different dosing schedules- weekly (28 day cycle), biweekly (28 day cycle) or dosing on day 1 and day 8 of a 3-weekly (21 day cycle) and in combination with pembrolizumab. There are four parts to this study. Part A is a dose escalation in patients with select advanced solid tumors primarily designed to evaluate safety and tolerability of BT8009 as monotherapy or in combination with pembrolizumab and to determine a recommended Phase II dose (RP2D). Following a selection of an RP2D, Part B, a dose expansion portion, will be initiated with the primary objective of clinical activity of BT8009 as a monotherapy or in combination with pembrolizumab in patients with select advanced solid tumors. Additionally Parts B-8 and B-9 will evaluate the safety and tolerability of an alternate dose and schedule of BT8009 monotherapy. Part C will evaluate safety and tolerability of RP2D in patients with renal insufficiency. Part D will further characterize the pharmacokinetics of BT8009 and MMAE.