The Patho-histogenesis And Early Events Of Ovarian Epithelial Neoplasm

Background and study purpose:The malignant ovarian epithelial neoplasm is the most common and lethal gynecological malignancy. In the past, tremendous efforts have been made to identify the precursor lesions of the disease in the ovary, aiming for early diagnosis and early intervention strategy. However, due to the limited understanding of the patho-histogenesis of the disease, the attempt to improve the overall survival has not been successful. In the most recent decade, it was discovered that the precursor lesions of majority of malignant ovarian tumors were non-ovarian. In general, ovarian carcinoma is a cohort of various subtypes of carcinomas with heterogeneous morphology, immunophenotypes and molecular genetic features. The current widely accepted classification of ovarian cancers is to divide the disease into 2 types:type 1 and type 2.Ovarian mucinous carcinoma is classified as type 1 ovarian carcinoma, together with low-grade serous carcinoma, low-grade endometrioid carcinoma, mucinous carcinoma, seromucinous carcinoma, clear cell carcinoma and Brenner tumor. Endometrioid carcinoma, clear cell carcinoma and seromucinous carcinoma were found to be associated with endometriosis. Unlike the aforementioned tumors, the histogenesis of the mucinous tumors is largely unsettled. As there is no benign mucinous counterpart found in normal ovary anatomy, the cell of origin of the majority of ovarian mucinous tumor remains enigmatic.Both ovarian mucinous tumor and Brenner tumor are classified as type 1 ovarian tumor. It has also been recently proposed that a sub-group of mucinous tumors may be derived from Brenner tumors, as the morphological association of a mucinous tumor with a Brenner tumor is frequently observed. Several recent studies revealed that up to 25%-30% of Brenner tumor is accompanied by ovarian mucinous tumor. However, molecular evidence supporting the hypothesis of tumor-tumor association is extremely limited.There is another subset of ovarian mucinous tumor, including ovarian mucinous carcinoma, described to be associated with ovarian mature teratoma and is hypothesized to be derived from the mucinous epithelium in teratoma and thus of germ cell origin. Unlike other ovarian epithelial malignancies, especially high grade serous carcinoma, ovarian mucinous carcinoma frequently affects in young women, among whom many are younger than 30 years old, making it one of the ovarian tumors with the youngest patient age besides germ cell tumors. As reported, there are up to 11% of ovarian teratoma associated with mucinous tumor. The lack of benign mucinous counterpart in normal ovary anatomy leads to the hypothesis that ovarian mucinous carcinoma associated with teratoma could be derived from the mucinous epithelium of intestinal phenotype in the teratoma but molecular evidence supporting the hypothesis is limited. Ovarian mucinous carcinoma associated with teratoma often shares the immunophenotype of mucinous carcinoma of gastrointestinal origin (CK7-/CK20+or CK7+<CK20+) and differ from that of "pure" ovarian mucinous carcinoma (CK7+/CK20-or CK7+>CK20+). As teratoma is the most common germ cell tumor in ovary, the two co-existing tumors could still be clonally unrelated "collison" tumors or the mucinous carcinoma in ovary is a metastatic lesion from gastrointestinal tract.In addition, primary ovarian mucinous tumor is the entity of ovarian tumor of the largest tumor size, with a mean size of 10cm. In cases of combined teratoma and mucinous tumor or mucinous carcinoma, the lesion of teratoma is usually focal and disproportionally smaller than the massively mucinous component. Therefore there is not unlikely that teratoma component be compressed and obliterated by the expanding mucinous neoplasm. For those pure primary mucinous carcinoma occurred in young women, the possibility of germ cell origin is worthy of being investigated.Therefore, the first part of the study is designed into 2 parts to explore the histogenesis of ovarian mucinous tumor associated with Brenner tumor and teratoma. respectively. The study is to investigate the clonal relationship between combined mucinous tumor and Brenner tumor in the same ovary, combined mucinous carcinoma and mature teratoma in the same side of ovary and the genotyping of primary ovarian mucinous carcinoma unassociated with mature teratoma in young and older patients to explore if primary ovarian mucinous carcinoma in young patients could be of germ cell origin.In the recent decade, great advances have been made in the histogenesis and pathogenesis of type 2 ovarian epithelial tumor, especially high grade serous carcinoma. Ovarian high grade serous carcinoma is a highly aggressive and deadly gynecological malignancy, which accounts for 90% of all ovarian serous carcinoma. It has been found in recent decade that the precursor lesion of a lot of high grade serous carcinoma is non-ovarian. The putative precursor lesions are located at fallopian tube fimbria, namely serous tubal intraepithelial carcinoma (STIC) and p53 signature, the latter likely represents the clonal expansion of tumor initiating cells. The phenotype of tumor initiating cells and early event in the pathogenesis of ovarian high grade serous carcinoma is unclear.Tumor-initiating cells are thought to be stem cells derived from somatic cells, or early progenitor cells acquired stem cell characteristics, sharing features with normal somatic stem cells. Being an important factor in retinoic acid signaling pathway, aldehyde dehydrogenase isoform 1A1 (ALDH1A1) is involved in cell self-renewal regulation and normal stem cell differentiation and is an extensively studied putative stem cell maker. In mice model, stem cells located at the ovarian hilum area have been found to express ALDH1A1 and are prone to malignant transformation. The potential significance of this interesting finding to human beings is still unknown.Study method:1, In Part 1A of the study, analysis of the two components of combined Brenner and mucinous tumors was undertaken by using a human androgen receptor gene (HUMARA) assay. Microsatellite genotyping was also performed in combined ovarian Brenner and mucinous tumor and mature cystic teratoma by analyzing various microsatellite loci. Immunohistochemistry staining was performed to evaluate the PAX8 expression in this subset of tumor. In Part 1B of the study, microsatellite genotyping was performed by using a variety of short tandem repeat makers and analyzed allelotypes of 8 mucinous tumors associated with a teratoma to determine whether they were clonally related. Human androgen receptor gene (HUMARA) assay was performed to further evaluate the clonality relationship of the case with unmatched genotype. Molecular genotyping was performed in pure ovarian mucinous carcinomas occurred in young patients (13-30 years old) and old ones (41-67 years old).2, In Part 2 of the study, immunohistochemistry was performed to assess the distribution pattern of ALDH1A1 staining in the epithelium of human fallopian tubes, with particular investigation in the tubal-mesothelial junction area, ovarian surface epithelium, putative precursors of ovarian high-grade serous carcinoma (serous tubal intraepithelial carcinoma and p53 signatures) and high grade serous carcinoma. In silico analyses of the mRNA expression data set from The Cancer Genome Atlas was performed. ALDH1A1 transcripts in high-grade serous carcinoma was compared to that of normal tubal epithelium and correlated with overall survival.Results:1, In Part 1A of the study, all eight informative cases of ten showed a concordant X-chromosome inactivation pattern between the two tumor components, indicative of a shared clonal origin (p=0.0039). Microsatellite genotyping in five of the combined tumors displayed an identical heterozygous pattern with paired Fallopian tube tissue, indicative of a somatic cell origin. In addition, paired box protein 8, a highly sensitive Miillerian epithelial marker, was not detected by immunohistochemistry in either tumor component in any of the ten tumors, suggesting that this subset of mucinous tumors does not originate from Mullerian-derived epithelium. In Part 1B of the study,7 of the 8 mucinous tumors showed complete or a high degree of homozygosity. Among the 6 pairs of tumors with teratoma tissue available for comparison,5 of 6 (83.3%) showed a high or complete degree of allelotypes matching, which differed from the somatic allelotypes of the normal control tissue. A discrepancy was detected between carcinoma and teratoma in one pair at several loci, with different X-chromosome inactivation patterns revealed by the HUMARA clonality assay. We also investigated the allelotypes of 16 ovarian mucinous carcinomas without a teratoma in young patients (range 13-30) and in 6 older patients (range 40-67) using the same method. None of these tumors showed pure homozygosity. The number of homozygous loci in this cohort was significantly lower than that in the first.2, In Part 2 of the study, Expression of ALDH1A1 was observed in tubal epithelial cells (including secretory and ciliated cells), tubal-mesothelial junctions as well as ovarian surface epithelium. In contrast, ALDH1A1 was not expressed in serous tubal intraepithelial carcinoma and p53 signatures. Positive staining in high-grade serous carcinoma was only presented in scattered tumor cells. In silico analyses of the mRNA expression data set from The Cancer Genome Atlas revealed ALDH1A1 transcripts was down-regulated in high-grade serous carcinoma when compared to normal fallopian tubal epithelium. The association between ALDH1A1 expression levels and overall survival was not observed.Conclusion:The first part of the study demonstrates that in primary ovarian mucinous tumors, there is a subset clonally related to ovarian Brenner tumor. In combined mucinous and Brenner tumors, the two different tumor components shared the same histogenesis. This subset of mucinous tumor is of somatic cell origin, not a germ cell origin. On the other hand, another subset of ovarian mucinous tumor associated with a teratoma is derived from the teratoma but occasionally they could be collision tumors. In addition, the majority of pure ovarian mucinous carcinomas in young women in whom a teratoma is not present are not derived from a teratoma. The second part of the study demonstrates that loss of expression of ALDH1A1 is an early event in the development of high-grade serous carcinoma. The study does not support ALDH1A1 as a specific marker of stem cells in human fallopian tube. Further searching for specific markers of Mullerian epithelial stem cells is warranted to identify the somatic stem cell population involved in the pathogenesis of high grade serous carcinoma.