PQ203 in Advanced Malignant Tumors Including Triple Negative Breast Cancer

This is an open-label, first-in-human study designed to evaluate the safety, tolerability, pharmacokinetics, and preliminary antitumor activity of PQ203 in patients with selected advanced solid tumors. PQ203 will be administered as a once-weekly intravenous infusion. The study consists of two parts: Phase 1A (dose escalation/expansion) and Phase 1B (dose optimization). * Phase 1A will employ a dose-escalation design in patients with advanced solid tumors to assess the safety and tolerability of PQ203 as monotherapy and to establish a provisional Recommended Phase 2 Dose (RP2D). A dose-expansion component will further evaluate the provisional RP2D in one or more selected tumor types. * Phase 1B will assess the provisional RP2D and further characterize safety, pharmacokinetics, and preliminary efficacy. Endpoints: * Primary Endpoints: Incidence of treatment-emergent adverse events (TEAEs) and determination of the RP2D. * Secondary Endpoints: Pharmacokinetic profile of PQ203 and its payload (MMAE), and preliminary evidence of antitumor activity.