Introduction Mature teratomas with diminutive foci of immature neural epithelium should not be diagnosed as immature teratomas. Inter-observer reproducibility in pathological diagnosis of immature teratoma and its association with clinical factors are unclear.

Methods This retrospective study aimed to identify biomarkers that predict the malignant potential of immature ovarian teratomas (UMIN000046404). A total of 148 cases diagnosed as immature teratomas from 21 institutions were included. A pathologist, blinded to clinical information, performed the central pathological review. Out of 148 cases, 102 were diagnosed as immature teratomas (Immature Group), 44 as mature teratomas (Mature Group), and 2 were excluded as they did not fulfill the inclusion criteria of the study. Clinical information of the cases was analyzed.

Results Age was lower in the immature group (median, 22.5 years, range 2–44) than in the mature group (28, 11­–48) (p=0.01, Student’s t-test). Salpingo-oophorectomy of the affected adnexa was performed in 90 (88%) and 17 (39%) cases in the immature and mature groups, respectively (p<0.01, Fisher Exact test); while the remaining underwent tumor resection, preserving the affected ovary. Three (2.9%) and 22 (50%) cases in the immature and mature groups, respectively, underwent laparoscopy (p<0.01, Fisher’s Exact test).

Conclusion/Implications Patients misdiagnosed with immature teratoma at primary institutions but centrally diagnosed with mature teratoma tended to be older, had undergone laparoscopy, and had the affected ovary preserved. Cases with a preoperative clinical diagnosis of mature teratoma and a postoperative pathological diagnosis of immature teratoma warrant further consultation from expert pathologists.