Case ReviewUndifferentiated Endometrial Carcinoma—Diagnostic and Therapeutic ChallengesLee, Yow-Shan MD∗; Lee, Cheng-Han MD, PhD, FRCPC†,‡ Author Information From the ∗Department of Family Medicine, Cathay General Hospital, Taipei, Taiwan †Department of Laboratory Medicine and Pathology, Royal Alexandra Hospital ‡Department of Laboratory Medicine and Pathology, University of Alberta, Edmonton, Alberta, Canada. Reprints: Cheng-Han Lee, MD, PhD, FRCPC, Department of Laboratory Medicine and Pathology, University of Alberta, 5-142E, Katz Bldg, 114th St and 87th Ave, Edmonton, Alberta, Canada T6G 2E1. E-mail: [email protected]. The authors have no funding or conflicts to declare. AJSP: Reviews & Reports: 9/10 2022 - Volume 27 - Issue 5 - p 208-211 doi: 10.1097/PCR.0000000000000525 Buy Metrics Abstract Undifferentiated/dedifferentiated endometrial carcinoma is clinically highly aggressive, particularly when it is defined by inactivation of core SWI/SNF proteins (co-loss of ARID1B, loss of SMARCA4, or loss SMARCB1 expression). We report here the case of a 37-year-old woman who presented with menorrhagia and the subsequent pathologic and clinical workup showed an advanced-stage ARID1A/ARID1B-deficient mismatch repair–proficient undifferentiated endometrial carcinoma. Despite pelvic external beam radiation and platinum/taxane-based chemotherapy (4 of 6 planned cycles), the patient experienced disease progression with osseous metastasis to her left elbow and died of her disease 7 months after clinical presentation. This case highlights the diagnostic and treatment challenges associated with such undifferentiated/dedifferentiated cancer types of the endometrium. Copyright © 2022 Wolters Kluwer Health, Inc. All rights reserved.