Clear Cell Carcinoma Arising From Adenomyotic Cyst: A Case Report

Clear cell carcinoma often arises from endometriosis, primarily from ovarian chocolate cysts and much less frequently from adenomyosis. We herein report a case of clear cell carcinoma arising from adenomyotic cyst in a 38-year-old woman, gravida 0, para 0, who was referred to our department with a diagnosis of a uterine tumor. Her medical history was unremarkable. Contrast-enhanced magnetic resonance imaging revealed a 13-cm uterine tumor with a predominantly hypointense signal on both T1- and T2-weighted images, accompanied by a hyperintense lesion in the center on T1-weighted images. Additionally, typical uterine leiomyomas were observed. Her serum CA125 (reference range: 0-35 units/ml) and CA19-9 (reference range: 0-37 units/ml) levels were elevated to 1,200 and 8,178 U/mL, respectively. Degenerated myoma was suspected preoperatively. Given the patient's desire to preserve her fertility, a myomectomy was performed. Macroscopically, the tumor was solid, white, and fibroid-like but contained chocolate-colored fluid. Pathological examination revealed clear cell carcinoma characterized by adenocarcinoma cells with clear and eosinophilic cytoplasm and nuclear atypia arranged in a tubulocystic pattern. Endometriosis was also found within the tumor. Subsequently, a hysterectomy, bilateral salpingo-oophorectomy, and pelvic and para-aortic lymphadenectomy were performed. No malignancy was detected in the resected uterus or adnexa, but metastasis to a para-aortic lymph node was observed. Based on these findings, the patient was diagnosed with stage IIIC2 endometrial cancer (pT1bN2M0, clear cell carcinoma) and received postoperative adjuvant therapy with paclitaxel and carboplatin. Eighteen months later, her serum CA125 increased to 45 U/mL, and a contrast-enhanced computed tomography scan revealed multiple liver and left supraclavicular lymph node metastases. Five cycles of pembrolizumab and lenvatinib followed by four cycles of doxorubicin and cisplatin were ineffective. The patient died 13 months after the diagnosis of recurrence.