Background We aimed to investigate the correlation of maximum standardized uptake value (SUVmax) with pathological characteristics of main tumor and to determine a Tumor/ Lymph node (T/LN) SUVmax ratio predicting metastasis to lymph nodes in NSCLC patients. statistically significant higher imply SUVmax, quantity of mitosis and advanced N stages compared to adenocarcinoma. The etiology of 100 PET/CT positive lymph node stations were metastasis in 14, anthracosis in 40, reactive in 39, granulomatous in 4, and silicosis in 3 patients. A T/LN SUVmax ratio of 5 or lower was suggestive for any malignant lymph node with a sensitivity of 92.8% and specificity of 47%. Conclusions SUVmax of a primary tumor is related to certain pathological characteristics, such as largest diameter, histology, and quantity of mitosis. A T/LN SUVmax ratio lower than 5 predicts the metastasis to lymph nodes with a high sensitivity. Background Non-small cell lung malignancy (NSCLC) is usually a heterogeneous group of carcinomas with different biological behaviors and prognoses. Histological classification and staging are crucial in constituting a treatment CP-724714 enzyme inhibitor strategy and predicting prognosis for NSCLC [1]. [18?F]-2-fluoro-deoxy-D-glucose (FDG)-positron emission tomography (PET) is usually a metabolic imaging technique which has become an essential tool for staging of NSCLC patients. The integration of PET with computed tomography (PET/CT) provides an accurate anatomic localization and improved staging especially for mediastinal lymph nodes and occult distant metastases [2,3]. It also provides prognostic information, monitors response to therapy and can be used to follow up patients after treatment [4]. The rationale for using FDG-PET in oncology is usually its ability to measure increased glucose metabolism of tumor cells. Elevated FDG uptake suggests that the lesions or tissues harbor tumor cells. The maximum standardized uptake value (SUVmax) greater than 2.5 is often used as a slice off value for malignancy. However it has been shown that there is a significant quantity of false positivity (due to inflammatory diseases) and false negativity (due to low-grade malignancies) in the evaluation of main tumor [5]. The major reasons of false negative and false positive lymph nodes are microscopic metastasis beyond the spatial resolution of PET/CT and lymph node involvement by underlying inflammatory processes such as immune reaction due to the presence of lung CP-724714 enzyme inhibitor tumor, obstructive pneumonia, anthracosis or granulomatous inflammation [6-8]. It is often assumed that FDG uptake is usually primarily within the malignant tumor cells, and SUVmax is usually a well known measure indicating the aggressiveness of tumor [9,10]. But other cellular components of such as normal parenchymal cells, atypical cells, inflammatory cells, fibroblasts, or hematopoietic progenitor cells may also uptake FDG. To the best of our knowledge, there is only one study investigating the correlation between SUVmax CP-724714 enzyme inhibitor and specific cellular components of the tumor conducted in patients with resected stage 1 NSCLC. In that study the authors found that the cellular composition of the tumor was highly variable and there wasnt any correlation between a specific tumor cellular component and FDG activity [11]. SUVmax of the primary tumor is usually a risk factor for occult mediastinal metastasis in clinical stage 1 NSCLC patients [12-14]. The likelihood of lymph node metastasis increases with the increase of tumor SUVmax [6,15]. SUVmax of lymph node is IL6ST also important for predicting metastasis, but false positivity is an important challenge [6,7]. For this reason some authors claimed to use a higher SUVmax value instead of the traditional value of 2.5 in order to increase the accuracy for presence of metastasis [7]. In this study we aimed to investigate the correlation of tumor CP-724714 enzyme inhibitor SUVmax value with largest tumor diameter, tumor histology, differentiation, quantity of mitosis, degree of stromal inflammation and necrosis, and to determine whether a T/LN SUVmax ratio can predict the presence of metastasis in mediastinal or hilar lymph nodes in NSCLC patients. Methods Patients Eighty-one chemotherapy and/or radiotherapy naive NSCLC patients with a PET/CT examination at the time of initial staging who subsequently underwent surgical resection were retrospectively evaluated. Among them 77 were male and 4 were female with a imply age of 59.8??8?years (range: 38-74). Fifty-five patients underwent lobectomy, 25 patients pneumonectomy and 1 individual wedge resection with total ipsilateral hilar and mediastinal lymph node dissection. Pathological stage was decided according to 7th edition of TNM staging system [1]. Demographic data of the patients, histopathological diagnosis, T and.