Abstract
Background: Nuclear protein in testis (NUT) carcinoma is a rare, aggressive, and poorly differentiated epithelial malignancy characterized by the rearrangement of NUTM1 (NUT midline carcinoma family member 1) on 15q14. It primarily originates along the midline structures, including the head, neck, thorax, and mediastinum. Although NUT carcinoma of the pelvic gynecological organs is exceedingly rare, reported cases have been limited to primary or metastatic ovarian tumors. Here, we present the first documented case of primary uterine NUT carcinoma. Case presentation: A 53-year-old postmenopausal woman presented with abnormal uterine bleeding and a uterine mass. She underwent a total abdominal hysterectomy with bilateral salpingo-oophorectomy. The initial postoperative histopathological evaluation suggested undifferentiated endometrial sarcoma; however, subsequent immunohistochemical (IHC) analysis and fluorescence in situ hybridization revealed NUTM1 rearrangement, confirming the diagnosis of NUT carcinoma. The patient experienced tumor recurrence six months postoperatively and succumbed to the disease nine months later. Discussion: The pathological diagnosis was challenging; the presence of abrupt squamous differentiation prompted further IHC analysis, leading to the definitive diagnosis. Primary uterine NUT carcinoma may be misdiagnosed as other undifferentiated uterine tumors due to its rarity and histological overlap. Conclusions: Given the diagnostic challenges, NUT IHC staining and molecular testing for NUTM1 rearrangement should be considered in undifferentiated uterine tumors with ambiguous histopathological features.