Successful treatment of advanced squamous cell carcinoma arising from mature cystic teratoma of the ovary with homologous recombination deficiency: A case report

Background: Squamous cell carcinoma arising from mature cystic teratoma of the ovary (MCT-SCC) has a poor prognosis at advanced stages. Although the relationship between the homologous recombination deficiency (HRD) status and platinum-based chemotherapy sensitivity or poly (ADP ribose) polymerase (PARP) inhibitor efficacy in epithelial ovarian cancer has been demonstrated in clinical trials, the significance of the HRD status in MCT-SCC remains unclear. Case presentation A 73-year-old woman with no remarkable past medical history was referred to our hospital for a huge left ovarian tumor. Laparotomy was urgently performed due to tumor rupture. We performed total abdominal hysterectomy, bilateral salpingo-oophorectomy, and partial omentectomy. The ovarian tumor was strongly adherent to the surrounding pelvic organs and could not be completely resected. The postoperative diagnosis was stage IIIB MCT-SCC (pT3bNXM0) of the left ovary. After surgery, we conducted the myChoice CDx and microsatellite instability (MSI) tests. The genomic instability (GI) score of 87 was remarkably high, and there was no BRCA1/2 pathogenic mutation. In contrast, the MSI test was negative. After six courses of combination therapy with paclitaxel and carboplatin, the residual tumors had shrunk by 73% (target lesions: 85 mm to 23 mm) and SCC-Antigen levels decreased from 12.8 ng/ml postoperatively to 1.6 ng/ml at the end of the initial course of chemotherapy and remained in the normal range thereafter. We considered the complete removal of residual tumors feasible and performed interval debulking surgery (IDS). We performed residual tumor resection and pelvic and para-aortic lymphadenectomy, and the tumors were completely resected. Subsequently, the patient underwent two courses of the combination of paclitaxel, carboplatin, and bevacizumab, followed by maintenance therapy with olaparib and bevacizumab. Five months after IDS, no recurrence has been observed. Conclusion: To the best of our knowledge, this is the first reported case of MCT-SCC with HRD-positive status. Although its frequency is unknown, platinum-based chemotherapy followed by maintenance therapy with oraparib and bevacizumab could be one of the promising treatment options for MCT-SCC.