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Thymomas sometimes require treatment for various recurrence patterns, despite their relatively good survival rates after resection. We focused on their maximum standardised uptake value (SUVmax) on preoperative 18F-fluorodeoxyglucose positron emission tomography as a tumour recurrence predictor in completely resected thymomas. Those with a high SUVmax might be at an increased recurrence risk, irrespective of tumour size. We categorised cases into axes (tumour size and SUVmax) and determined whether cluster analysis predicts recurrence patterns and freedom from recurrence (FFR). Of the 115 patients who underwent primary surgery for thymoma between 2005 and 2018, 66 were evaluated. According to the Masaoka stage and World Health Organization (WHO) histological type, all histological diagnoses were obtained after resection. All recurrences were diagnosed using computed tomography and categorised into three patterns: distant, local and regional recurrences. A multiple regression analysis was carried out to identify predictors for each recurrence pattern. Cluster analysis was carried out based on tumour size and SUVmax. The FFR rate was evaluated. All patients with preoperative SUVmax <3.4 were free from recurrence regardless of Masaoka stage, WHO histological classification and tumour size. Multiple regression analysis revealed that the SUVmax was the only significant predictor for distant recurrence. All cases were divided into three clusters. Cluster 3, with average tumour size and a high SUVmax, showed a higher risk of distant recurrence rate (60%) and a significantly lower FFR rate (P = 0.003). The preoperative positron emission tomography/computed tomography SUVmax could be a useful thymoma recurrence predictor, especially for distant recurrences. In addition, cluster analysis revealed that cases with average tumour sizes and extremely high SUVmax were identified to have a higher recurrence risk and a significantly lower FFR rate than those in other clusters. Even after complete resection, such cases should be closely followed-up and screened for distant recurrence. • Finding predictors for postoperative thymoma recurrence is important. • PET/CT is useful for predicting distant thymoma recurrences. • No study has examined the SUVmax of PET/CT impact on predicting completely resected thymoma recurrence regarding tumour size. [ABSTRACT FROM AUTHOR]