The clinicopathological characteristics and survival outcomes of primary expansile vs. infiltrative mucinous ovarian adenocarcinoma: a retrospective study sharing the experience of a tertiary centre.

BACKGROUND: Mucinous ovarian carcinomas (MOCs) are rare ovarian tumours accounting for 3% of all epithelial ovarian carcinomas (EOCs). They are either expansile or infiltrative, based on the tumour's histological pattern of invasion. MOCs have a distinct molecular profile, natural history, chemo-sensitivity, and prognosis compared to other EOCs. The aim of this study was to describe patient and tumour characteristics, as well as survival outcomes of expansile and infiltrative primary MOCs. METHODS: This was a retrospective cohort study conducted at a tertiary cancer centre. Patients had surgery for primary MOC between Jul 1, 2010 and Oct 28, 2022. All patients discussed at the Oxford multidisciplinary team (MDT) meeting with a diagnosis of MOC were included. We excluded patients with mucinous metastatic carcinoma (MMC), dual histological diagnoses, those who died before treatment was initiated, and patients with incomplete records. RESULTS: A total of 47 patients were identified and 14 were excluded. Out of the remaining 33 MOCs, 23 (70.6%) were expansile and 10 (30.4%) were infiltrative. The median follow-up was 37 months (95% CI: 14.1-69.8). Patients with infiltrative tumours were older than those with expansile tumours (median age 62 vs. 55 years, P=0.049). Infiltrative tumours were diagnosed at a more advanced International Federation of Gynaecology and Obstetrics (FIGO) stage compared to expansile tumours: FIGO stage II/III 50% vs. 8.2% (P=0.002). We found paired-box gene 8 (PAX8) more frequently expressed in expansile tumours (75% vs. 37.5%, P=0.099). Adjuvant treatment was administered in 50% of patients with infiltrative disease, compared to only 13% of those with expansile disease (P=0.036). 80% of patients who have relapsed had received adjuvant chemotherapy, compared to 17.2% of patients without relapse (P=0.012). At 3 years, there was a statistically significant difference in progression-free survival (PFS) (94.7% vs. 65.6%, P=0.02) between the expansile and infiltrative groups, but no difference in overall survival (OS) (88.8% vs. 90%, P=0.875). CONCLUSIONS: Patients with infiltrative tumours were older, more likely to have bilateral tumours and more likely to have an advanced FIGO stage at diagnosis. Adjuvant treatment was more likely to be administered to patients with infiltrative tumours, however, this did not prevent relapse. PFS at 3 years was significantly higher in patients with expansile tumours. PAX8 was more frequently expressed by expansile tumours.