Analysis of chromosome 12p over-representation and clinicopathological features in mediastinal teratomas

Teratomas show diverse biologic behaviour and prognosis as well as variable histological features. Importantly, post-pubertal testicular teratomas composed of mature components have a potential for malignant behaviour, in contrast to ovarian dermoid cysts and pre-pubertal testicular teratomas which are considered almost always benign. On the other hand, the biological behaviour and histogenesis of extragonadal teratomas are still not fully elucidated. In this study of mediastinal mature teratoma (MT), we investigated clinicopathological features and chromosome 12 short arm (12p) status which constitutes a major genetic aberration in the germ cell tumours (GCT) and is indicative of malignant potential. A total of 123 cases of primary mediastinal MT were included, and clinical data were retrieved regarding demographic information, adjuvant treatment, post-operative clinical course, and level of serum tumour markers. Histopathological features were evaluated in 123 cases and 12p status was studied by FISH in 25 cases. Female predilection was identified in the post-pubertal group (38 males vs 77 females), and paediatric teratoma cases had longer follow-up (mean 62.2 months vs 26.5 months). All patients had excellent prognosis with no tumour-associated death, regardless of age and sex. None of the MT cases had cytological atypia and all 21 cases finally evaluated by fluorescence in situ hybridisation were negative for 12p over-representation. Our results support the benign nature of mediastinal MT and suggest the possibility that it may share a common histogenesis with pre-pubertal type GCTs.