YL211-INT-101-01

This is a multicenter, open-label, Phase 1 study. The study will enroll subjects with advanced solid tumors. It consists of six parts. Objectives for Dose-Escalation Parts (Part 1 and Part 4) To evaluate the safety and tolerability of YL211 as monotherapy in patients with selected advanced solid tumors (Part 1) and in combination with pembrolizumab in patients with second or third line locally advanced unresectable or metastatic non-squamous non-small cell lung cancer (NSCLC) (Part 4) To determine the maximum tolerated dose (MTD) and select the recommended expansion dose(s) (RED(s)) of YL211 as monotherapy in patients with advanced solid tumors (Part 1) and in combination with pembrolizumab in patients with second line locally advanced unresectable or metastatic non-squamous NSCLC (Part 4) Objectives for Backfill Enrollment Parts (Part 2 and Part 5) To better estimate and characterize the safety and efficacy of YL211 as monotherapy in patients with metastatic colorectal cancer (mCRC) or locally advanced unresectable or metastatic NSCLC (Part 2) and in combination with pembrolizumab in patients with previously untreated locally advanced unresectable or metastatic non-squamous NSCLC (Part 5) To select the RED(s) of YL211 as monotherapy in patients with metastatic colorectal cancer (mCRC) or locally advanced unresectable or metastatic NSCLC (Part 2) and in combination with pembrolizumab in patients with previously untreated locally advanced unresectable or metastatic non-squamous NSCLC (Part 5) Objectives for the Dose-Expansion Parts (Part 3 and Part 6) To further characterize the safety and efficacy of YL211 as monotherapy (Part 3) in patients with locally advanced unresectable or metastatic non-squamous or squamous NSCLC and in combination with pembrolizumab in patients with previously untreated locally advanced unresectable or metastatic non- squamous NSCLC (Part 6) To compare the clinical activity of YL211 in combination with pembrolizumab against pembrolizumab, pemetrexed, and platinum-based chemotherapy (cisplatin or carboplatin) in participants with previously untreated advanced unresectable or metastatic non-squamous NSCLC (Part 6)