Serum Vitamin D Levels as a Prognostic Biomarker in Patients Receiving Immune Checkpoint Inhibitors

Objective: Vitamin D exerts pleiotropic effects on tumor biology and immune regulation, including modulation of T-cell function and antigen presentation.Preclinical evidence suggests that optimal vitamin D status may enhance immune checkpoint inhibitor (ICI) efficacy; however, data are limited among ICI-treated patients.We aimed to evaluate the prognostic significance of baseline serum 25(OH)D levels in patients receiving ICIs. Material and Methods:A retrospective cohort of 244 patients with advanced solid tumors treated with ICI.Baseline serum 25(OH)D concentrations, obtained within 30 days prior to ICI initiation, were categorized as sufficient (>20 ng/mL), insufficient (12-20 ng/mL), or deficient (<12 ng/mL). Results:The median age of the patients was 63 years; 65.2% were male.The most common tumor types were non-small cell lung cancer (32.8%), renal cell carcinoma (18.9%), and melanoma (14.3%).Vitamin D status was sufficient in 36.5%,insufficient in 34.8%, and deficient in 28.7% of patients.In multivariable analysis, vitamin D deficiency independently predicted shorter overall survival (OS) [hazard ratio (HR): 2.264, 95% confidence interval (CI): 1.553-3.300;p<0.001] compared with the vitamin D-sufficient group.Both vitamin D insufficiency (HR: 1.494; 95% CI: 1.067-2.092;p=0.019) and vitamin D deficiency (HR: 2.0; 95% CI: 1.411-2.833;p<0.001) were independently associated with inferior progression-free survival (PFS). Conclusion:Baseline vitamin D deficiency is an independent adverse prognostic factor for OS and PFS in ICI-treated patients.Integrating vitamin D assessment into pretreatment evaluation may facilitate risk stratification and inform supportive care strategies, warranting prospective validation.