Chapter 13: Epithelial Ovarian Cancers: Low Malignant Potential and Non-Serous Ovarian Histologies

INTRODUCTION

Epithelial ovarian cancer is the leading cause of death from gynecologic cancers and the fifth leading cause of all cancer-related deaths among women. The American Cancer Society estimates that 21,880 new cases of ovarian cancer will be diagnosed and 13,850 women will die of the disease in the United States in 2010.¹ Approximately 90% of epithelial ovarian cancers are derived from coelomic epithelium of the ovary, fallopian tube, or peritoneum. Epithelial ovarian cancers are heterogeneous and comprise a group of neoplasms that differ based on their histopathologic and molecular features, as well as their clinical behavior.^2,3 These include low malignancy potential (LMP) tumors and frankly invasive malignant neoplasms. Malignant ovarian cancers can be further subdivided into 2 distinct groups based on their morphologic and molecular genetics features. Type I tumors include low-grade serous, mucinous, low-grade endometrioid, clear cell, and transitional (Brenner) carcinomas. Conversely, type II tumors include high-grade serous carcinoma, high-grade endometrioid carcinoma, malignant mixed mesodermal tumors (carcinosarcomas), and undifferentiated carcinomas.⁴ Type II tumors are characterized as highly aggressive, evolving rapidly, and uniformly having poor outcomes. In contrast, LMP and type I tumors tend to be diagnosed at an earlier stage, behave in an indolent fashion, and have a better prognosis.

EPIDEMIOLOGY

Key Points

1. Women with mucinous, endometrioid, clear cell, and low-grade serous ovarian cancers present at a younger age than women with high-grade serous ovarian, tubal, and peritoneal cancers.

2. Mucinous, endometrioid, clear cell, and low-grade serous cancers progress in a stepwise manner from precursor lesions to invasive disease.

3. Type I and type II ovarian cancers may be distinguished by specific and distinct genetic alterations.

Approximately 15% to 20% of all epithelial neoplasms are LMP (also referred to as borderline) tumors, and type I tumors account for 25% of malignant epithelial ovarian cancers (Figure 13-1).^{4,5, and 6} High-grade serous ovarian, primary peritoneal, and tubal carcinomas are treated in a similar fashion and are discussed in Chapter 12. The histologic subsets of both type I and II tumors comprise 42% serous, including 2% to 10% low-grade serous carcinomas, 7% to 20% endometrioid, 17% undifferentiated, 3% to 12% clear cell carcinoma, and 3.5% to 12% mucinous (Figure 13-2).^{6,7,8,9,10,11,12, and 13} Transitional-cell tumors consist of both Brenner tumors and transitional-cell carcinomas and are exceedingly rare. Only 2% of all epithelial ovarian cancers are Brenner tumors.