Marginal calcification of thymoma: differences in the location of calcification indicate differences in the characteristics of thymomas

BACKGROUND: Thymic epithelial tumors (TETs) are the most common tumors located in the anterior mediastinum. Calcification is sometimes observed in thymomas, especially in thymomas, and has been reported to be an indicator of the invasive behavior of thymomas. However, whether or not all calcification indicates invasive behavior is unclear. The present study therefore analyzed the location, size, and patterns of thymoma calcification and the relationships between calcification and clinicopathological factors and prognosis. METHODS: We conducted a retrospective study among 77 thymoma patients who underwent surgery between January 2012 and May 2022 and analyzed the relationship between the location of calcification and clinicopathological findings. The patients were categorized into three groups: those with inner calcification of the tumor (group I), those with marginal calcification (group M), and those without any calcification (group N). RESULTS: Calcification was identified in 13 thymomas (16.9%) in group I (n=8) and group M (n=5). Group M included significantly more low-risk thymomas than the other groups (P=0.030). In low-risk thymomas, especially type AB thymoma, marginal calcification was observed more frequently than in other lesions. There were significant differences in age (P=0.024) and Masako-Koga stage (P=0.020) among the groups. In group I, younger patients and patients with advanced-stage disease were included. There were no significant differences in the rates of recurrence or the recurrence-free period among the groups. However, recurrence was not recognized in any members of group M. CONCLUSIONS: The location of calcification should be a point of focus in thymomas, and differences in the location of calcification indicate differences in the characteristics of thymomas.