Ovarian clear cell adenocarcinoma revealed in a young patient during hormone therapy: a case report

Ovarian cancer arising from an ovarian endometriotic cyst is frequently encountered; however, this condition has rarely been reported in young patients. We herein report a case of malignant transformation of an ovarian endometriotic cyst in a 26-year-old woman (gravida 0, para 0). During the initial examination at our hospital, ultrasound revealed an endometriotic cyst in the right ovary measuring 49×44×29 mm and an endometriotic cyst in the left ovary measuring 59×53×32 mm with no marked mural nodules on either side. The patient was followed up every 3 months while receiving hormone therapy. At the 6-month follow-up, ultrasound revealed 10-mm mural nodules within the endometriotic cyst of the left ovary. At 10 months, ultrasound revealed that these the mural nodules had enlarged to 15 mm. Pelvic magnetic resonance imaging revealed that the tumor in the left ovary was 64×63 mm in size, which was slightly larger than in the previous scan. The patient underwent laparotomy because of the potential for malignant transformation. Pathological examination revealed clear cell adenocarcinoma. Although malignant transformation of this cancer is rare in women in their 20s, its possibility should be considered; this is true even when cyst enlargement can be controlled during hormone therapy. Magnetic resonance imaging is extremely useful in the diagnosis of malignant transformation.