This retrospective study was reviewed and approved by the Human Ethics Committee of Kinan Hospital (Approval No. 283: Clinical outcomes of endoscopic surgery: retrospective analyses, 2024/4/23).

The deidentified medical records of 298 patients who underwent laparoscopic surgery for OCs between July 1, 2010 and December 31, 2024 were retrospectively reviewed. Patients who underwent laparoscopic surgery based on an almost definitive preoperative diagnosis of OECs or OMCTs—these diagnoses being the primary indications for surgical intervention—were excluded. Additionally, patients whose MRI findings suggested only the possibility of these conditions, specifically, 14 patients with OECs, 16 patients with OMCTs, 16 patients with ovarian fibromas, 2 patients with ovarian haemorrhage, and 5 patients with pelvic masses of unknown origin, were also excluded. Furthermore, 6 patients whose MRI suggested the presence of solid components were excluded, resulting in a total of 59 excluded patients. All 239 cases were subsequently classified as Bo/Ma-OT or Be-OT, with any patient having even a small portion of Bo/Ma-OT in the pathological diagnosis categorized as Bo/Ma-OT. In this study, Bo-OT and Ma-OT were grouped together as Bo/Ma-OT, as the likelihood of a Ma-OT being identified postoperatively was extremely low, occurring in 3 of 239 patients. This classification allowed for a meaningful comparison with Be-OT. Data from the 239 patients included in the analysis were collected, and the following variables were extracted: (1) basic patient characteristics, such as age, body mass index (BMI), parity, gynaecological surgical history, smoking history, and dysmenorrhea; and (2) OC-related data, such as tumour size (defined as the maximal diameter measured on MRI), carbohydrate antigen 19-9 (CA19-9) expression, carbohydrate antigen 125 (CA125) expression, and coexistent leiomyoma. Additionally, data on 5 MRI-related features were extracted from the radiologists’ interpretation reports: bilateral cysts, multilocular cysts, septal enhancement, suspected mucinous tumours, and suspected adnexal torsion. Comparisons of operation time and blood loss were conducted for reference only, as this study included data from patients treated with various surgical methods, including salpingo-oophorectomy (187 patients), cystectomy (38 patients), unilateral salpingo-oophorectomy with contralateral cystectomy (7 patients), salpingectomy (4 patients), salpingectomy with cystectomy (1 patient), and adhesiolysis (2 patients). This comparison included patients with coexistent hysterectomy (1 patient) or myomectomy (1 patient), as well as 3 patients who underwent laparoscopically-assisted surgery, which was considered equivalent to laparoscopic surgery in the analysis.

First, we compared the basic characteristics, including age, BMI, parity, tumour size, operation time, and blood loss, between patients undergoing Bo/Ma-OT and those undergoing Be-OT. We then performed the Shapiro-Wilk test for these six variables: in the Bo/Ma-OT group (n = 26), age (W = 0.94, p = 0.11) and BMI (W = 0.95, p = 0.30) showed normal distributions, while parity (W = 0.89, p 0.05), tumour size (W = 0.85, p 0.01), operation time (W = 0.88, p 0.01), and blood loss (W = 0.32, p 0.01) did not. In the Be-OT group (n = 213), all six variables showed non-normal distributions (age: W = 0.97, p 0.01; BMI: W = 0.96, p 0.01; parity: W = 0.89, p 0.01; tumour size: W = 0.87, p 0.01; operation time: W = 0.92, p 0.01; blood loss: W = 0.38, p 0.01). Therefore, we compared the two groups using medians and the Wilcoxon rank-sum test. Next, after selecting 16 factors from variables realistically available in the medical records, with reference to previous reports [9], the 239 patients were divided into two groups based on the presence or absence of each factor. The proportions of patients undergoing Bo/Ma-OT (n = 26) were subsequently compared between the two groups. In particular, multiple features of tumour were compared. Tumour diameters of 10 cm and 15 cm were used as reference thresholds; however, a 20-cm cut-off was not feasible, as only 12 of the 239 tumours exceeded this size. In addition, as the descriptions of menstruation were sometimes unclear, “menopause” was defined as “age 50 years or older”, and complaints such as “irregular menstruation”, “heavy menstrual bleeding”, and “severe menstrual pain” were collectively categorized as “menstrual disorders”.

Finally, candidates for multivariate analysis were selected based on a p-value 0.05 in the univariate comparisons. As including all 16 factors in the multivariate analysis would result in an excessive number of variables, the p-value threshold was set to identify the factors most likely to be relevant. We then extracted data regarding the following 3 factors: (1) multilocular cyst; (2) septal enhancement; and (3) suspected mucinous tumour. In addition, the 15-cm threshold, which had the smaller p-value, was selected as the criterion for the ninth factor of “large tumour”. Multivariate logistic regression analysis was then performed via JMP version 18 for Windows (SAS Institute, Inc., Tokyo, Japan), based on binary data (0 or 1) collected for each factor for each patient in an Excel sheet, to estimate the likelihood of Bo/Ma-OT.

Statistical analyses were performed using Microsoft Excel 365 (Microsoft Corporation, Redmond, WA, USA) and JMP version 18 for Windows. Associations between patient characteristics and the likelihood of Bo/Ma-OT diagnosis were assessed using the Wilcoxon rank-sum test, the Pearson chi-square test, and multivariable logistic regression analysis. Odds ratios (ORs) and 95% confidence intervals (95% CIs) were calculated to quantify the strength of these associations. A p-value 0.05 was considered statistically significant.

The final diagnoses determined by pathological examination are summarized in Table 1. Among the 239 cases, 26 were classified as Bo/Ma-OT, and their patient characteristics were compared with those of the 213 patients with Be-OT.

In the simple comparison of patient characteristics, no significant differences were found between the Bo/Ma-OT and Be-OT groups (Table 2). Operation time was used for reference only, as the surgical approaches varied across cases. However, a trend toward a difference in operation time was observed. As shown in Table 3, simple analysis of the associations between each factor and the likelihood of Bo/Ma-OT identified 4 significant factors: multilocular cyst, septal enhancement, suspected mucinous tumour, and tumour size $\ge$15 cm.

Among the candidate factors selected based on the simple analyses, none differed significantly between the groups (Table 4). Only septal enhancement had p-value 0.1.