Study Population: Adult subjects aged 18-75 years with relapsed/refractory advanced solid tumors (including liver, gastric, colorectal, ovarian cancer, etc.) and malignant ascites confirmed by cytology, who have failed at least 2 lines of standard systemic therapy.
Study Design: This is a dose-escalation, single-center, open-label, prospective Phase 1 study. A total of 18 subjects will be enrolled and assigned to 2 administration groups (9 subjects each):
Group A (Intravenous infusion): For subjects with small-volume malignant ascites.
Group B (Intraperitoneal perfusion): For subjects with large-volume symptomatic malignant ascites.
Each group will follow a conventional "3+3" dose-escalation design with 3 dose levels (1×10⁹, 3×10⁹, 6×10⁹ NK cells per dose), administered once weekly, 3 weeks per cycle, for 2 consecutive cycles.
Primary Objectives: To evaluate the safety and tolerability, and to determine the dose-limiting toxicity (DLT) of NK521 administered intravenously and intraperitoneally.
Secondary Objectives: To assess the preliminary anti-tumor efficacy including objective response rate (ORR), disease control rate (DCR), progression-free survival (PFS), overall survival (OS), duration of response (DOR), puncture-free survival (PuFS), and changes in tumor markers, as well as health-related quality of life (HRQoL).