Ovarian cancer is the most lethal gynecologic malignancy. Efforts at early detection and new therapeutic approaches to reduce mortality have been largely unsuccessful because the origin and pathogenesis of epithelial ovarian cancer are poorly understood. Despite numerous studies that have carefully scrutinized the ovaries for precursor lesions, none have been found. This has led to the proposal that ovarian cancer develops de novo. Studies have shown that epithelial ovarian cancer is not a single disease but is composed of a diverse group of tumors that can be classified based on distinctive morphologic and molecular genetic features. One group of tumors, designated type I, is composed of low-grade serous, low-grade endometrioid, clear cell, mucinous and transitional (Brenner) carcinomas. These tumors generally behave in an indolent fashion, are confined to the ovary at presentation and, as a group, are relatively genetically stable. They lack mutations of TP53 but each histologic type exhibits a distinctive molecular genetic profile. Moreover, the carcinomas exhibit a shared lineage with the corresponding benign cystic neoplasm often through an intermediate (borderline tumor) step, supporting the morphologic continuum of tumor progression. In contrast, another group of tumors, designated type II, are highly aggressive, evolve rapidly and almost always present in advanced stage. Type II tumors include conventional high-grade serous carcinoma, undifferentiated carcinoma and malignant mixed mesodermal tumors (carcinosarcoma). They displayTP53 mutations in over 80% of cases and rarely harbor the mutations that are found in the type I tumors. Recent studies have also provided cogent evidence that what have been traditionally thought to be primary ovarian tumors actually originate in other pelvic organs and involve the ovary secondarily. Thus, it has been proposed that serous tumors arise from the implantation of epithelium (benign or malignant) from the fallopian tube. Endometrioid and clear cell tumors have been associated with endometriosis, which is regarded as the precursor of these tumors. Since it is generally accepted that endometriosis develops from endometrial tissue by retrograde menstruation it is reasonable to assume that the endometrium is the source of these ovarian neoplasms. Finally, preliminary data suggest that mucinous and transitional (Brenner) tumors arise from transitional-type epithelial nests at the tubal-mesothelial junction by a process of metaplasia. Appreciation of these new concepts will allow for a more rationale approach to screening, treatment and prevention which potentially can have a significant impact on reducing the mortality of this devastating disease.

Malignant cells, like all actively growing cells, must maintain their telomeres, but genetic mechanisms responsible for telomere maintenance in tumors have only recently been discovered. In particular, mutations of the telomere binding proteins alpha thalassemia/ mental retardation syndrome X-linked (ATRX) or death-domain associated protein (DAXX) have been shown to underlie a telomere maintenance mechanism not involving telomerase (alternative lengthening of telomeres), and point mutations in the promoter of the telomerase reverse transcriptase (TERT) gene increase telomerase expression and have been shown to occur in melanomas and a small number of other tumors. To further define the tumor types in which this latter mechanism plays a role, we surveyed 1,230 tumors of 60 different types. We found that tumors could be divided into types with low (<15%) and high (≥15%) frequencies of TERT promoter mutations. The nine TERT-high tumor types almost always originated in tissues with relatively low rates of self renewal, including melanomas, liposarcomas, hepatocellular carcinomas, urothelial carcinomas, squamous cell carcinomas of the tongue, medulloblastomas, and subtypes of gliomas (including 83% of primary glioblastoma, the most common brain tumor type). TERT and ATRX mutations were mutually exclusive, suggesting that these two genetic mechanisms confer equivalent selective growth advantages. In addition to their implications for understanding the relationship between telomeres and tumorigenesis, TERT mutations provide a biomarker that may be useful for the early detection of urinary tract and liver tumors and aid in the classification and prognostication of brain tumors.

BACKGROUND-Ovarian clear-cell and endometrioid carcinomas may arise from endometriosis, but the molecular events involved in this transformation have not been described.