This Phase 1b trial is an open-label, multi-center study of XMT-1592 administered as an intravenous infusion once every 3 weeks. The dose-escalation (DES) segment of the study will establish the expansion (EXP) dose and is intended to establish the maximum tolerated dose (MTD) or recommended Phase 2 dose (RP2D) for XMT-1592 in patients with high grade serous ovarian cancer (HGSOC) or non-small cell lung cancer (NSCLC), adenocarcinoma subtype. The EXP segment of the study will consist of 2 parallel cohorts of patients (HGSOC and NSCLC) to confirm the MTD or RP2D and estimate the objective response rate in each selected patient population. In DES, the observation period for dose-limiting toxicities is 21 days, between Day 1 through the end of Cycle 1 which includes the pre-dose assessments before receiving the Cycle 2 dose. All adverse events (AEs) will be graded according to NCI, CTCAE v5.0). In general, AEs Grade 3 are dose-limiting toxicities with some modifications.