This 20-year retrospective observational study has identified an incidence of metachronous contralateral mature ovarian teratoma during follow-up of just 2% (95% confidence interval 0–6%). This is a lower rate compared to similar retrospective European studies [a–6]. In the largest of these, Braungart et al. demonstrated an incidence of 4% (7/177) among patients treated in UK specialist centres . Other single-centre studies which have featured smaller sample sizes than our own have reported higher rates of metachronous contralateral tumours including 13% (4/30) in a French series and 23% (5/22) in a series from Finland [5, 6]. Data from North America have also demonstrated a low incidence, though study design and clinical practice appear to differ from that in the UK. In Canada, Rogers et al. reported 66 children and adolescents undergoing ovarian cystectomy at a single centre and identified just one case (2%) of metachronous contralateral teratoma, which interestingly occurred in association with an ipsilateral recurrence . In a single-centre study performed in the USA, Templeman et al. identified no cases of metachronous contralateral disease among their sample of 52 patients under 21 years of age . It should be noted, however, that only six (12%) underwent elective ultrasonography postoperatively.
Of note, one patient had a raised preoperative AFP with benign histology on examination of the surgical specimen. She was unfortunately lost to follow-up, so no further biochemical testing was performed and her raised tumour marker remains unexplained. There was variation in formal postoperative follow-up in our series, with a median surveillance period of 7 months and a minority of patients receiving no postoperative imaging. Similar variation has been identified in previous European and North American studies [4,5,6, 8, 9]. This variation in follow-up contributes to ongoing uncertainty regarding the actual incidence of metachronous contralateral tumours. However, appreciation that this is a clinically relevant phenomenon has resulted in development of surveillance protocols in some jurisdictions, including the UK since 2018 . The importance of surveillance and early detection and treatment is twofold. It is hoped that early detection prior to the point at which a tumour becomes clinically evident will increase the possibility of complete resection prior to other complications developing (e.g., transformation to immature tumour, local mass effect). Secondly, it is anticipated that removal of a smaller tumour detected during surveillance may increase the possibility of ovarian sparing resection. Since many index tumours are large at the time of presentation and treated with oophorectomy, ovarian sparing surgery in the case of a metachronous contralateral tumour may be the only possibility of a girl maintaining her native fertility.
The current challenge to those developing surveillance guidance however is the ongoing uncertainty regarding the natural history of this condition in terms of true incidence of contralateral metachronous disease and the timescale over which this may happen. Any surveillance program requires resources, has a cost implication and carries the possibility of introducing anxiety. Thus, surveillance must be justifiable and should be informed by adequate data. The current UK guidance is based on just one series with an incidence of 23%. The majority of other published series, including this one, report a lower incidence. Furthermore, the UK guidance recommends surveillance for a 10-year period after primary tumour resection but metachronous contralateral tumours have been detected up to 14 years later [4, 5]. Currently, the optimal design of a surveillance program is uncertain due to the lack of adequate data and, in particular, a lack of data with complete follow-up over a long time period [4,5,6, 8]. The principal limitation to this study is that there was variation in follow-up with a relatively short median period of 7 months. As such, it is possible that the true incidence of metachronous contralateral tumour may be higher than we have detected. However, we believe this is unlikely since we are the only centre in our region to whom cases of ovarian pathology are referred. It remains possible however that other cases exist. As with other single-centre studies, the small sample size limits the accuracy with which we can estimate the true incidence of metachronous contralateral teratoma. However, we report one of the largest single-centre series to date and include patients over a 20-year period.