BACKGROUND: Pain is one of the most common symptoms in patients suffering from advanced cancer and receiving palliative care and is often responsible for a poor quality of life. To date, there exists no published correlation between biological, measurable biomarkers and pain intensity. OBJECTIVES: The primary objective was to search and identify pain-associated cytokines (biomarkers) correlating with changes in numeric rating scale (NRS) pain scores in patients with cancer before and after pain treatment. The secondary objectives were to assess cytokine serum level differences between patients and healthy controls and to evaluate possible relationships between pain entities, pain intensity (in NRS), gender, location of primary tumor, and the patients' cytokine baseline concentrations. STUDY DESIGN: Controlled, prospective study. SETTING: University medical center. METHODS: Eligible patients with exacerbated cancer-related pain (NRS = 5) and healthy controls with no pain were included. Serum level changes of 19 cytokines were analyzed before and during opioid treatment. RESULTS: Of 19 analyzed biomarkers, 5 (IL-7, IL-18, MCP-1, MIP-1α, MIP-1β and OPG) turned out to correlate significantly with pain relief. In healthy controls, all analyzed cytokines showed no significant differences. In the secondary analysis, only one significant correlation was detected between OPG and pain entities. Furthermore, IL-4, IL-7, IFN-γ and OPG appeared to account for the ability to predict a patient's gender. LIMITATIONS: Our findings should be considered as preliminary and need to be confirmed in further studies. CONCLUSION: Our results provide preliminary evidence of a significant correlation of pain relief in patients with cancer and at least 5 cytokines. These biomarkers may serve as the basis for development of diagnostic tools for pain assessment and could serve as potential new targets for pain control.