Ovarian cancer – modern approach to its origin and histogenesis

Abstract

Ovarian cancers (OC) belong to a heterogeneous group of pathologies and are traditionally classified with regard to histological type and degree of differentiation. OC was hypothesized to originate from ovarian surface epithelium (OSE) and inclusion cysts epithelium (IC). Unfortunately, this theory was never supported by any clinical or molecular evidence linking carcinogenesis with OSE and was refuted. OC subtypes demonstrate morphologic features that resemble Müllerian duct-derived epithelia of the genital tract. Investigations of the HOX gene family, Müllerian epithelial differentiation markers, confirmed the HOX genes expression in many subtypes of OC but not in OSE. The first step towards connecting OC origin with other than OSE genital tract structures were epidemiological observations indicating a minor OC risk after tubal ligation in women with the BRCA mutation. The first in situ carcinoma was found in the Fallopian tube fimbriae. Further research confirmed the same mechanism in sporadic OC. Endometriosis and endometrium cells may be a highly probable place of endometrioid OC initiation. Mucinous types share common futures with gastrointestinal tract cancers and there one needs to search for their precursors. Clear cell carcinoma may arise from glandular epithelium of endocervix or from endometrioid foci. The new classification of OC was proposed in 2004, suggesting to divide all OC into two types: I and II. Type II includes serous and endometrioid G3 subtypes, carcinosarcomas and undifferentiated OC. They are responsible for 75% of OC morbidity, identified usually in FIGO stages III or IV, have poor prognosis and relapse early. The remaining hystiotypes, with better prognosis and earlier FIGO stages at time of diagnosis, were classified as type I. Serous and endometrioid poorly differentiated ovarian cancers demonstrate mutation in TP53 gene (type II) and highly differentiated ones, generally, in BRAS and KRAS genes (type I). The differences in molecular pathways also confirm different patterns of carcinogenesis of both OC types. Modern approach to OC histogenesis and origin emphasizes the necessity to verify OC screening, detection and treatment methods.