Molecular and therapeutic stratification of endometrioid ovarian carcinoma
Epithelial ovarian carcinomas (EOC) comprise five main histological subtypes, each displaying distinct pathological, molecular and clinical characteristics. Endometrioid ovarian carcinomas (EnOC) account for 10% of EOC and have been historically under-investigated. They typically present as early stage, grade 1 or 2 (low grade) tumours arising from endometriosis, and are associated with excellent clinical outcomes. However, Grade 3 (high grade) EnOC, as well as the even rarer de-differentiated carcinomas, can be challenging to differentiate from high grade serous ovarian carcinomas (HGSOC) based on morphology alone. Through the refinement of EnOC diagnostic criteria, several studies have now demonstrated that many previously diagnosed high grade EnOC are in fact HGSOC. This is further supported by gene expression profiling studies demonstrating that a proportion of high grade EnOC cluster together with HGSOC. As such, true high grade EnOC are increasingly rare and are associated with poor prognosis. WT1 immunohistochemistry (IHC) is a useful tool to discriminate high grade EnOC (WT1 negative (WT1-ve)) from HGSOC (WT1 positive), reducing inter-observer variation. To date, clinical and molecular characterisation of EnOC has been confounded by the inclusion of historically misclassified HGSOC in older studies. Mutational analysis performed by more recent studies have either only been applied to low grade EnOC, or lack information on grade or diagnostic criteria used. As a result, the molecular landscape and clinical behaviour of EnOC, in particular high grade EnOC, is not well defined. In this study, tumours historically diagnosed as EnOC were identified through the Edinburgh Ovarian Cancer Database. Contemporary pathology review was performed utilising WT1 and p53 IHC. WT1-ve EnOC of all grades, and WT1-ve tumours with high grade serous and undifferentiated morphology were identified and included in the primary analysis. Clinical characteristics of the primary cohort were extracted from the database. Survival analysis was performed and responses to chemotherapy and endocrine therapy recorded. 63 tumours from the primary cohort underwent DNA extraction and whole exome sequencing (WES); comprising all WT1-ve tumours with mutant p53 expression on immunohistochemistry (p53mut(IHC)) (n=28), all WT1-ve high grade carcinomas with p53 wild-type expression on immunohistochemistry (p53wt (IHC)) (n=12) alongside a randomly selected subset of WT1-ve p53wt (IHC) low grade EnOC tumours (23 of 87 cases, 26.4%). Supervised mutational and copy number analysis was performed across 75 commonly mutated genes previously reported in endometrial, ovarian or pan cancer studies and molecular subgroups were identified. Unsupervised clustering analysis validated these molecular subgroups. Hormone receptor expression levels (oestrogen receptor (ER), progesterone receptor (PR) and androgen receptor (AR)) were evaluated as histoscores in the primary cohort. Multivariable survival analysis, accounting for stage, residual disease, decade of diagnosis. grade and age, was performed on resulting molecular and hormone receptor subgroups. Between May 1980 and December 2013, 125 WT1-ve tumours were identified. Overall five year disease specific survival (DSS) was 73.2% with the most favourable prognosis in those with early stage disease. Five year DSS in patients with advanced stage p53wt (IHC) low grade EnOC was 50.0%. Late relapses beyond five years were common in early stage disease. Patients with stage IV disease had poor prognosis with median DSS of less than one year. Radiological and CA125 response rates to platinum based chemotherapy in evaluable tumours was 44.5% and 69.3%, respectively. Median duration of endocrine therapy in evaluable tumours was 317 days (range 35 – 615 days). Of the 61 tumours successfully sequenced, TP53 mutations (TP53mut) were the most common (45.9%); followed by mutations in EnOC-associated genes (ARID1A (41.0%), CTNNB1 (31.1%), PTEN (24.6%) and PIK3CA (23.0%)). Only TP53mut status was independently associated with shortened DSS (HR=0.35, 95% CI 0.14-0.83, P=0.018). Copy number analysis revealed significantly more alterations in the TP53mut tumours compared to TP53wt tumours (P <0.0001), with a particular enrichment of variation across EnOC-associated genes in the TP53mut subgroup with no EnOC-associated gene mutations. The majority of the primary cohort expressed ER and PR whereas AR expression was low. A PR histoscore of >150, when compared to a PR histoscore ≤ 150, was found to be independently associated with DSS, whereas no associations were observed with ER or AR expression levels. In particular, patients with stage II EnOC and a PR histoscore of >150 displayed a ten year DSS of over 90%. Through this study, TP53 mutation status and a PR histoscore of greater than 150 were identified as independent predictors of survival. This demonstrates EnOC to be a heterogeneous disease with distinct molecular and hormone receptor subgroups that demonstrate differential clinical outcome. Patients with TP53 mutated and/or low PR expression EnOC have inferior prognosis and the development of novel therapeutic agents should be focused on these groups which display the greatest unmet need.