Microinvasion links ovarian serous borderline tumor and grade 1 invasive carcinoma

Ovarian serous borderline tumor (SBT) and grade 1 (low grade) serous carcinoma are closely related, but, unlike SBT which has been well studied, there have been few studies looking primarily at grade 1 serous carcinoma. The objective of this study was to better understand the relationship between serous borderline tumors and grade 1 serous carcinomas.

We performed a clinicopathologic review of 46 women with SBT and 16 with grade 1 serous carcinoma.

Thirteen of forty-six (28%) SBTs had a micropapillary pattern, 12/46 (26%) had evidence of microinvasion and 19/46 (41%) had extraovarian implants, of which 1/19 (5%) was invasive. Three of forty-six (7%) of SBTs recurred, all of which were originally advanced stage. No patient with a microinvasive SBT recurred. The 16 grade 1 serous carcinomas divided into those with evidence of coexisting SBTs (5 cases) and those without (11 cases). Nine of sixteen (56%) carcinomas recurred, comprising 5/5 with SBT and 4/11 without. All patients had advanced stage at diagnosis. Microinvasion, invasive implants and recurrences all showed qualitative histologic resemblance to carcinoma. There were no micropapillary areas in any of the carcinomas, although cribriform pattern was seen in these tumors.

Advanced stage at diagnosis was the most important prognostic marker in patients with SBT. Although a micropapillary pattern was common, it did not adversely affect prognosis per se, but was associated with a higher stage. A micropapillary pattern was not seen adjacent to microinvasion or in association with grade 1 serous carcinoma. Microinvasion was common but, in our series, did not appear to worsen the prognosis. Grade 1 serous carcinoma was less common than SBT and had a more unfavorable prognosis. The qualitative histologic similarity between microinvasion, invasive implants, recurrences and grade 1 serous carcinoma suggests that microinvasion represents early invasion and is not just another histologic pattern of SBT. We speculate that some invasive implants and recurrences may be peritoneal grade 1 serous carcinoma.