PD‐1/PD‐L1 Inhibitors Plus Chemotherapy Versus Chemotherapy Alone as First‐Line Therapy for Patients With Unfavorable Cancer of Unknown Primary: A Multicenter, Retrospective Cohort Study

This multicenter study aimed to investigate the efficacy and safety of PD-1/PD-L1 inhibitors plus chemotherapy (ICI-Chemo group) versus chemotherapy alone (Chemo group) for patients with cancer of unknown primary (CUP) in the first-line setting. We included patients with unfavorable CUP across four medical centers in China. Between January 2014 and December 2023, 117 patients were enrolled: 46 patients in the ICI-Chemo group and 71 patients in the Chemo group. After a median follow-up of 28.1 months, the ICI-Chemo group exhibited a significant improvement over the Chemo group in median PFS (9.10 months vs. 6.37 months; hazard ratio [HR] 0.46; 95% CI: 0.30-0.71; <i>p</i> < 0.001) and OS (35.67 months vs. 10.2 months; HR 0.37; 95% CI: 0.22-0.64; <i>p</i> < 0.001). Similarly, among patients who received TP (taxane plus platinum)-based chemotherapies, OS and PFS benefits were observed in the ICI-Chemo group. The objective response rate was higher in the ICI-Chemo group than in the Chemo group (54.35% vs. 22.53%, <i>p</i> < 0.001). Grade 3 or higher drug-related adverse events occurred in 11 patients (23.91%) in the ICI-Chemo group and 28 patients (39.44%) in the Chemo group. Thus, PD-1/PD-L1 inhibitors plus chemotherapy could be the preferred first-line treatment for patients with unfavorable CUP, providing improved efficacy and manageable toxicity.