Squamous Cell Carcinoma Arising in a Mature Cystic Teratoma of the Ovary: A Case Report

Mature cystic teratoma (MCT) is a common benign ovarian germ cell tumor, although malignant transformation occurs rarely in 1-2% of cases, most frequently into squamous cell carcinoma (SCC).Bilateral MCTs with malignant transformation occurring in only one ovary are uncommon.A 46-year-old perimenopausal woman presented with incomplete bladder emptying and lower abdominal pain.Clinical evaluation revealed several features associated with malignant transformation, including age >40 years, a large mass (12.2 cm), bilateral MCTs, and markedly elevated cancer antigen 125 (CA-125) at 185.9 U/mL.The patient underwent total abdominal hysterectomy with bilateral salpingo-oophorectomy (TAH-BSO), with histopathology confirming malignant transformation into moderately differentiated SCC within the left ovarian MCT capsule, with intact tumor protein 63 (p63) and p40 nuclear positivity supporting the squamous phenotype, alongside a benign right ovarian MCT.Postoperative positron emission tomographycomputed tomography (PET-CT) showed no evidence of metastatic disease, and serum CA-125 decreased to 35.0 U/mL.She subsequently received adjuvant carboplatin and paclitaxel chemotherapy and remained without evidence of disease at 6-month follow-up.This case highlights the importance of considering malignant transformation in perimenopausal women with large, bilateral MCTs and elevated tumor markers.