Primary invasive mucinous epithelial ovarian carcinoma (MOC) is a rare subtype of epithelial ovarian carcinoma (EOC). According to the 2020 World Health Organization (WHO) classification, the invasive patterns of MOC are classified into two categories: Infiltrative and expansile invasion. Studies examining the relationship between expansile and infiltrative primary MOCs are limited. In our local setting, there are no published studies to determine the impact of classifying primary MOCs between the two subtypes to treatment outcomes. This study, therefore, aims to determine the prevalence of primary MOC subtypes, their clinical and demographic characteristics, and clinical outcomes.

This is a retrospective study of patients diagnosed with MOCs for a 5-year period from January 2013 to December 2017 in a public end-referral tertiary hospital. A pathological review was conducted using the 2020 WHO classification to determine the pattern of invasion. Demographic data were obtained and the treatment outcome of infiltrative invasion and expansile invasion of ovarian mucinous carcinoma were compared. Log–rank test was used to determine the overall survival (OS) with the specific type of MOCs.

A total of 29 cases were included in this study wherein 79.3% were expansile MOC type and 20.7% were infiltrative. Most of the patients had International Federation of Gynecology and Obstetrics Stage IA (27.6%). All patients had laparotomy and half of the patients received adjuvant therapy, 47.8% and 50% in expansile and infiltrative type, respectively. The factors associated with overall mortality were MOC type: expansile, hazard ratio (HR) = 0.3, 95% confidence interval (CI) = 0.07–0.91, P = 0.047, and infiltrative, HR = 3.3, 95% CI = 1.1–13.5, P = 0.047. Median OS was significantly higher in patients with expansile compared to infiltrative type (42 vs. 25 months, P = 0.039).

Infiltrative invasion was observed to be a prognostic factor showing worse outcomes for ovarian mucinous carcinoma compared to expansile invasion.