Real-world evidence on the influence of sex, age, and tumour type on pembroli-zumab-associated adverse reaction reporting remains limited. We retrospectively ana-lysed individual case safety reports (ICSRs) submitted to EudraVigilance between 1 January and 31 December 2025 involving pembrolizumab monotherapy. Adverse re-actions were classified according to MedDRA System Organ Class (SOC), and toxicity burden was defined as single- versus multiple-SOC involvement. Associations were assessed using Pearson’s chi-square test and Cramér’s V; sex comparisons across nine SOCs used a Bonferroni-adjusted threshold of p< 0.0056. Overall, 8,488 ICSRs were an-alysed; sex was available in 7,991 reports, age in 6,941, and 6,482 were evaluable across 14 tumour types. Overall toxicity burden did not differ by sex (p=0.110). Endocrine (18.4% vs 12.4%) and blood and lymphatic disorders (13.4% vs 9.5%) were more frequent in women, whereas respiratory (12.4% vs 7.0%) and cardiac disorders (13.9% vs 11.5%) were more frequent in men, all remaining significant after Bonferroni correction. However, none persisted after adjustment for tumour histotype and age (adjusted ORs: 1.06, 0.85, 1.22 and 1.02, respectively). Multiple-SOC reporting differed modestly by age, being lower in individuals >85 years (39.9% vs 47.7% and 48.1%; p=0.026), and by tumour type (p=0.016). Effect sizes were small. Observed sex-related reporting patterns may therefore largely reflect tumour-type composition rather than an independent sex effect. Findings are exploratory and require confirmation in denominator-based prospective studies.