Introduction Ultrastaging in endometrial cancer (EC) led to increased detection of isolated tumor cells (ITC, ≤0.2 mm) and micrometastases (MM, 0.2‐2 mm), with unclear effect on prognosis. Our aim was to characterize the impact of ITC and MM on the outcome of these patients. Methods Grade 1 to 2 stage I endometrioid EC patients with nodal ITC (n = 11) or MM (n = 12) between 2012 and 2018 were retrospectively compared to a matched group of lymph node negative (n = 18) patients based on age, body mass index, grade, myometrial invasion, and lymphovascular space invasion (LVI) status using propensity score analysis (1:1). Mann‐Whitney U tests were performed on continuous variables and χ2 tests on categorical variables. Progression‐free survival (PFS) was the main endpoint. Results All MM and 81% of ITC had LVI. More ITC/MM patients received RT and chemotherapy (91.7% vs 18.4%; 70.8% vs 4.5%, respectively; P < 0.01) without significant difference in treatment‐related toxicities (25% vs 27.3% grade 1%‐2% and 20.8% vs 9.1% grade 2‐3; P = 0.538) or PFS (29.2 vs 25 months; P = 0.828). Two distant recurrences occurred in MM patients after 2.5 years; one lung and one para‐aortic lymph node. Conclusion With adjuvant treatment, ITC/MM in otherwise well‐differentiated stage I endometrial cancer have similar outcomes to matched LN− patients.

Background: Approximately 2–6% of endometrial cancers (ECs) are due to Lynch Syndrome (LS), a cancer predisposition syndrome caused by germline pathogenic variants (PVs) affecting the DNA mismatch repair (MMR) pathway. Increasingly, universal tissue-based screening of ECs has been proposed as an efficient and cost-effective way to identify families with LS, though few studies have been published on Canadian cohorts. The purpose of this study was to evaluate the feasibility and overall performance of a universal immunohistochemistry (IHC) screening program for women with EC within a single Canadian university hospital centre. Methods and Results: From 1 October 2015 to 31 December 2017, all newly diagnosed ECs (n = 261) at our centre were screened for MMR protein deficiency by IHC. MMR deficiency was noted in 69 tumours (26.4%), among which 53 had somatic MLH1 promoter hypermethylation and were considered “screen-negative”. The remaining MMR-deficient cases (n = 16) were considered “screen-positive” and were referred for genetic counselling and testing. Germline PVs were identified in 12/16 (75%). One additional PV was identified in a screen-negative individual who was independently referred to the Genetics service. This corresponds to an overall LS frequency of 5.0% among unselected women with EC, and 6.4% among women diagnosed under age 70 years. Our algorithm detected MMR gene pathogenic variants in 4.6% and 6.2% of unselected individuals and individuals under age 70 years, respectively. Four germline PVs (30.8%) were identified in individuals who did not meet any traditional LS screening criteria. Conclusions: Universal IHC screening for women with EC is an effective and feasible method of identifying individuals with LS in a Canadian context.