TFEB‑altered renal cell carcinomas are rare neoplasms, frequently mimicking other tumors. Although FISH remains the diagnostic gold standard, its limited availability has prompted the evaluation of light microscopy‑based ancillary markers. This study compares the performance of immunohistochemistry and RNA‑ISH in detecting TFEB‑altered renal cell carcinomas and distinguishing them from other renal neoplasms. Sixteen FISH/molecularly confirmed TFEB‑altered renal cell carcinomas (12 rearranged, 4 amplified) were analyzed by immunohistochemistry for TFEB (3 different clones), cathepsin K (clone 3F9), and GPNMB, and RNA‑ISH for TRIM63 and TFEB. Forty-eight clear cell renal cell carcinomas, 48 papillary renal cell carcinomas, 72 chromophobe renal cell carcinomas, 48 oncocytomas, 5 TFE3‑rearranged renal cell carcinomas, and 4 FLCN/mTOR-mutated renal cell neoplasms served as controls. Staining patterns and diagnostic performance were assessed and compared. TFEB immunohistochemistry demonstrated variable sensitivity, with the Bethyl assay showing the greatest reliability. Cathepsin K (clone 3F9) and GPNMB displayed high sensitivity but lacked specificity, labeling 40% and 50% of TFE3‑rearranged tumors, respectively, and subsets of common renal neoplasms. Similarly, TRIM63 RNA‑ISH was strongly positive in all TFEB‑altered renal cell carcinomas but also in TFE3‑rearranged neoplasms. Instead, TFEB RNA‑ISH demonstrated exclusive expression in all TFEB‑altered renal cell carcinomas, with stronger signals in rearranged tumors, whereas it was negative in all control cases, including TFE3‑rearranged neoplasms. TFEB RNA‑ISH emerged as the most accurate light microscopy‑based method for detecting TFEB‑altered renal cell carcinomas, reliably distinguishing them from TFE3‑rearranged and other renal tumors, potentially representing a practical and cost‑effective alternative to FISH, particularly when molecular diagnostics are lacking.

Mature teratomas account for approximately 20% of all ovarian tumors identified in pathological studies. Benign or malignant somatic neoplasms developing within teratomas can arise from any tissue in up to 2% of mature cystic teratomas, including low-grade malignant mucinous neoplasms. This report presents the case of a 34-year-old woman with no previous gynecological or general health issues, who was admitted to our Hospital after an asymptomatic pelvic mass was detected during a routine exam. A transvaginal ultrasound revealed a unilateral pelvic mass in the left adnexal region, measuring 8 cm. The CT scan showed a cystic-appearing formation measuring nearly 12 cm, which indented the bladder dome. Final diagnosis indicated a mucinous carcinoma arising from a mucinous borderline lesion within the context of a mature ovarian teratoma. No other involvement or lymphadenopathies were detected on 18FDG-PET CT scan, and the patient is now well and free of recurrences.