Micropapillary serous carcinoma of the ovary. A distinctive low-grade carcinoma related to serous borderline tumors.

According to the International Federation of Gynecology and Obstetrics (FIGO) and the World Health Organization (WHO), stromal invasion, defined as destructive infiltrative growth, is the sole criterion used to distinguish serous borderline tumors from invasive serous carcinomas of the ovary. Although this criterion effectively identifies most malignant tumors, it does not permit the identification of a small subset of well-differentiated ovarian carcinomas that do not display destructive infiltrative growth but that may be associated with malignant behavior. In this study, we describe a group of such serous neoplasms that have distinctive morphologic features and that are often associated with progressive, invasive disease. We have designated these tumors micropapillary serous carcinomas (MPSC). They are characterized by a filigree pattern of highly complex micropapillae arising directly from large, bulbous papillary structures. The micropapillae are covered by round to cuboidal cells with a high nuclear-to-cytoplasmic ratio. Typical serous borderline tumors tend to display a hierarchical pattern of branching terminating in small papillae or tufts, and the cells covering the papillae tend to be more columnar and often ciliated compared with cells of MPSC. We reviewed more than 400 cases of serous ovarian borderline tumors and well-differentiated serous carcinomas and identified 26 cases of MPSC. Seventeen tumors lacked destructive infiltrative growth (noninvasive), and nine contained areas of invasion ranging from minimal to extensive. Eight of the 26 tumors were stage I, and none of the patients developed recurrence whether or not their tumors had demonstrable invasion. In contrast, of the 16 women presenting with stage II disease or higher and who had more than 1 year of follow-up, eight (50%) have either died of intra-abdominal carcinomatosis or are alive with carcinoma. Twenty-four (92%) of MPSCs contained areas of serous borderline tumor. The frequent association of MPSCs with serous borderline tumors suggests that MPSCs arise from the latter and may account for the few cases of serous borderline tumors that have been associated with progression to invasive carcinoma.