This is a randomized, open-label, active-controlled, multicenter Phase III trial evaluating QLC5508 versus docetaxel in participants with metastatic castration-resistant prostate cancer (mCRPC) who have progressed after prior treatment with novel hormonal agents (NHAs). Participants are randomized to receive either QLC5508 monotherapy (experimental arm) or docetaxel (control arm). The primary objective is to compare the efficacy of QLC5508 versus docetaxel, as measured by radiographic progression-free survival (rPFS) assessed by an Independent Radiological Review Committee (IRC).

Inclusion Criteria:

• Male, aged ≥18 years.
• Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1.
• Life expectancy of at least 3 months.
• Histologically or cytologically confirmed adenocarcinoma of the prostate without evidence of small-cell features.
• Diagnosis of metastatic castration-resistant prostate cancer (mCRPC).
• Prior treatment with novel hormonal agents (NHAs) and documented disease progression.
• Adequate organ function.
• Recovery from all reversible adverse events (AEs) related to prior anticancer therapies.

Exclusion Criteria:

• 1. Prior treatment with a B7-H3-targeted therapy, or with an antibody-drug conjugate (ADC) using a topoisomerase I inhibitor (TOP1i) as the payload, or with any TOP1i-class agent.

  2. History of or current significant cardiovascular or cerebrovascular disease. 3. Active, uncontrolled infection. 4. Concurrent or prior history of another primary malignancy 5. History of interstitial lung disease (ILD) or non-infectious pneumonitis, or current ILD/non-infectious pneumonitis 6. Current hepatic encephalopathy, hepatorenal syndrome, or cirrhosis classified as Child-Pugh class B or worse.

  7. Known hypersensitivity or allergy to any investigational product or its excipients.