case_images: PMC11345190_01
case_images: (A) Transvaginal ultrasonography showed a right ovary (arrow) measuring 3 cm in size. (B) The size of the right ovary (arrow) increased from 3cm to 6 cm with a three-and-a-half-month interval between examinations. (C) PET scan showed increased FDG accumulation of right ovary (arrow). (D) PET scan showed increased FDG accumulation of uterine cavity (arrow).
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case_images: During a routine ultrasound examination, a newly developed right ovarian tumor measuring 5.9 x 3.5 cm was detected, which had not been identified three and a half months earlier ( Figures 1A, B ). Figure 1C ). Focal FDG accumulation in the uterine cavity (SUVmax.eq = 4.7) was also observed, suggesting endometrial malignancy or physiological uptake ( Figure 1D ).
case_images: (A) Timeline of the patient's treatment process. (B) Endometrial lesion (arrow) measuring 1.3 cm observed in the endometrial cavity of uterus. (C) Enlarged right ovary (arrow) and normal ovary (arrowhead) noted during operation.
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case_images: A comprehensive staging surgery was performed ( Figures 2B, C ). The patient's treatment timeline is shown in  Figure 2A , illustrating the rapid progression of her disease despite progestin treatment.
case_images: (A) Pathology of endometrial biopsy confirmed atypical hyperplasia at initial diagnosis. (B) Representative microscopic photo demonstrating grade 2 endometrioid carcinoma (Hematoxylin and eosin stain). (C) Immunohistochemical stain showing MSH2 loss. (D) Immunohistochemical stain showing MSH6 loss.
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case_images: MSH6 and MSH2 were negative ( Figure 3 ). Microsatellite instability (MSI) testing by Next-Generation Sequencing (NGS) also confirmed to be MSI-high, with genetic variants at MSH2 (R711*, splice site 2006-2A>G) and MSH6 (F1088fs*2), concordant with immunohistochemistry (IHC) stain.