Molecular classification of metastatic and recurrent endometrial endometrioid carcinoma: prognostic relevance among low‐ and high‐stage tumours

Aims Molecular classification according to The Cancer Genome Atlas (TCGA) improves endometrial endometrioid carcinoma (EEC) prognostication and has specific treatment implications; however, original data were skewed towards low‐grade and low‐stage tumours. Herein, we molecularly classify EECs metastatic at the time of diagnosis or with subsequently documented recurrent/metastatic disease to examine correlation with clinical outcomes. Methods TCGA categories include POLE ‐mutated, microsatellite instability (MSI), p53 abnormal (p53 abnl) and no specific molecular profile (NSMP). POLE targeted sequencing at exons 9, 11, 13 and 14 and immunohistochemistry (IHC) for PMS2, MSH6 and p53 were performed to establish molecular classification. Results The distribution in our cohort of 141 EECs was similar to that generally reported in EEC, with nine POLE ‐mutated (6%), 45 MSI (32%), 16 p53 abnl (11%) and 71 NSMP (50%), with similar distributions between low‐ and high‐stage cohorts. We demonstrate that when stratified by molecular subtype, disease‐specific survival from the time of high‐stage (stages III–IV) presentation or time of recurrence in low‐stage (stages I–II) disease among metastatic and/or recurrent EEC is strongly associated with TCGA classification (high‐stage P = 0.02, low‐stage P = 0.017). Discordant molecular classification between primary and metastatic/recurrent tumours occurred in four of 105 (3.8%) patients, two related to PMS2/MSH6 IHC and two related to p53 IHC. Conclusions We demonstrate that molecular classification is prognostically relevant not only at the time of diagnosis, but also at the time of recurrence and in the metastatic setting. Rare subclonal alterations occur and suggest a role for confirming TCGA classification in recurrent/metastatic tumours.