Thymoma and the increased risk of developing extrathymic malignancies: a multicentre study.

Although thymoma is considered a relatively indolent neoplasia, patients affected by this disease are at high risk of developing second tumours (STs). The aim of this study is to assess the risk of developing STs after surgical thymoma resection. A multicentre retrospective study of patients operated on for thymoma within five Italian Thoracic Surgery Institutions, between 2000 and 2011, was conducted. The overall STs number and incidence were calculated. The number of metachronous STs was compared with the expected cancer number (ECN) in an Italian population, and the standardized incidence ratio (SIR) and 95% confidence intervals were calculated. Potential variables of STs predictors were also evaluated. There were 302 patients; myasthenia gravis (MG) was observed in 166 (55%) and other autoimmune syndromes in 49 of them. In 118 patients (39.1%), the Masaoka thymoma stage was greater than II and in 194, the WHO histological type ranged from B1 to C. Fifty STs were observed (28 metachronous, 4 synchronous and 18 detected before thymoma). The observed metachronous STs number was significantly higher than ECN. An increased risk of STs development was observed in advanced stage thymomas and in those with histological high grade. On the contrary, MG seems to be a protective factor in STs development. Our study confirms the high risk of developing STs in patients with thymoma. Aggressive forms of thymoma are those in which this risk appears to be more evident. The central role of an intrinsic immune system alteration might be the key to interpret this phenomenon.