Borderline epithelial tumors of the ovary

The concept and terminology of borderline epithelial tumors of the ovary have been controversial for over a century, in spite of the acceptance of a borderline category in almost all current classifications of ovarian tumors. Typically, borderline tumors are noninvasive neoplasms that have nuclear abnormalities and mitotic activity intermediate between benign and malignant tumors of similar cell type. Borderline tumors of all surface epithelial cell types have been studied. The most common and best understood are serous borderline tumors and mucinous borderline tumors of intestinal type, which are the subject of this review. Some of the most challenging issues for serous tumors include: the criteria and clinical behavior of stromal microinvasion; the high prevalence of synchronous extraovarian disease; the classification and histopathologic features of associated peritoneal tumor implants, especially invasive implants; and, the prognostic significance of micropapillary tumors. The mucinous borderline tumors of intestinal type have a different set of considerations, including: their frequently heterogeneous composition with coexisting benign, borderline and malignant elements; the classification and significance of accompanying noninvasive carcinoma; the recognition of stromal invasion, including microinvasion and expansile invasion; and, the historically misunderstood relationship to pseudomyxoma peritonei. All of these issues are discussed in this presentation, as are the important gross and microscopic features of serous and mucinous borderline tumors and pertinent information on their treatment and prognosis.