Cancer patients are at increased risk of severe COVID-19 outcomes. Understanding their immunological response to SARS-CoV-2 mRNA vaccination is essential for identifying molecular biomarkers that can predict vaccine efficacy. MiRNAs are promising biomarkers because they regulate immunity-related genes through virus-host interactions. This study aims to validate a specific miRNA profile in cancer patients to assess their immune response to COVID-19 vaccination and the influence of these miRNAs on humoral, cellular immunity and systemic inflammation. This study includes three cohorts: Cohort 1 (56 cancer patients with haematological and solid tumours) with blood samples collected before, -3 and − 6 months post-boost, Cohort 2 (209 cancer patients) and Cohort 3 (86 healthy individuals) with samples collected − 3 and − 6 months post-boost. Cellular immunity was evaluated in 104 cancer patients by measuring IFN-γ production post-booster vaccination. In solid cancer patients from Cohort 1, the expression of hsa-miR-7-5p, hsa-miR-15b-5p, and hsa-miR-98-5p increased three months after the booster dose and, in haematological patients, a similar trend was observed for hsa-miR-98-5p. When analysing all patients from cohorts 1 and 2, at -3 and − 6 months post-booster, a decrease in hsa-miR-7-5p was observed in solid cancer patients, while both hsa-miR-98-5p and hsa-miR-7-5p levels declined in haematological patients 6 months post-boost, possibly due to the declining of vaccine-induced inflammation. A significant positive Spearman correlation was found between hsa-miR-7-5p expression and IgG S levels. Additionally, IFN-γ non-reactive patients showed higher hsa-miR-7-5p levels compared to IFN-γ positive patients, suggesting a potential influence on both humoral and cellular immune response. Furthermore, patients with high expression of hsa-miR-24-3p exhibited significantly higher platelet-to-lymphocyte ratio (PLR) while high expression of hsa-miR-7-5p was significantly associated with elevated of both PLR and systemic immuno-inflammation index (SII) indices suggesting a potential correlation between these miRNAs and systemic inflammatory status. Accordingly, hsa-miR-7-5p may represent a key biomarker integrating immune and inflammatory regulation in cancer patients. Identifying potential biomarkers could enhance personalized medicine approaches, enabling more precise management of high-risk cancer patients while considering their influence on immune response development and systemic inflammation in the context of COVID-19 vaccination.