Non-small cell lung cancer (NSCLC) is one of the most common malignancies in the western world [1]. Despite multiple therapeutic and diagnostic advances, the overall survival is low and recurrence of NSCLC is a common problem with different treatment regimens. The inclusion of ¹⁸fluorine fluorodeoxyglucose (¹⁸FDG) positron emission tomography (PET) in combination with computed tomography (CT) in clinical practice was revolutionary for the staging of NSCLC [2]. ¹⁸FDG-PET/CT provides morphological, functional, and metabolic information about the tumor, which is usually highly, metabolically active. Due to the increased glucose uptake, ¹⁸FDG is actively accumulatedin the tumor tissues, resulting in an increased standardized uptake value (SUV). The tumor tissue itself consists of neoplastic cells, extracellular matrix, fibroblasts, and various immune cells. These immune cells include tumor-infiltrating lymphocytes, regulatory T cells, and macrophages. Macrophages have different activation patterns and play an essential role in inflammation and cancer. In particular, tumor-associated macrophages (TAMs) are a specialized group of alternatively activated or M2 macrophages. TAMs release several chemokines that are different from those released by classically activated macrophages found in an inflammatory environment. One of the most important chemokines released by TAMs is CC-chemokine ligand 18 (CCL18). Although CCL18 is present in healthy subjects, its levels are significantly elevated in the serum of patients with NSCLC. It correlates with overall survival and tumor stage in several malignant diseases [3,4]. A recurring problem is that increased glucose metabolism can be found in the inflammatory tissue, which can also lead to an increased SUV in ¹⁸FDG PET/CT, lowering its oncological specificity [5]. In a previous study, we demonstrated that serum CCL18 levels can be used to differentiate between patients with NSCLC and healthy subjects [3]. Hence, we investigated the correlation between serum CCL18 levels and the maximum standardized uptake value (SUV_max) of the primary tumor using ¹⁸FDG-PET/CT. We found a significant correlation between the SUV_max of the primary tumor and the serum CCL18 level. The data are important because they can be used to draw conclusions about immunometabolism. Furthermore, they can serve as basis for future prospective clinical studies.