Ovarian Endometrioid Borderline Tumor With Massive Squamous Differentiation: A Case Report

Abstract Introduction Ovarian endometrioid borderline tumor is uncommon and constitutes only 0.2% of all epithelial ovarian tumors. Many patients have associated endometriosis, and coexisting endometrial hyperplasia and/or carcinoma is commonly present. Methods Here we report an ovarian endometrioid borderline tumor with massive squamous differentiation. The peculiar histologic features made the diagnosis of this uncommon entity even more challenging. The patient was a 43-year-old female with a history of chronic pelvic pain. A pelvic ultrasound showed a 7.9-cm complex solid and cystic right ovarian mass and a hypoechoic left ovarian mass. Patient underwent a hysterectomy with bilateral salpingo-oophorectomy. Grossly, the right ovary showed a 2.5-cm solid and cystic lesion with focal papillary inner surface. Microscopic examination showed uterine adenomyosis with serosal endometriosis. The left ovary showed endometriosis with atypical hyperplasia. Initial representative sections from the right ovary demonstrated extensive squamous cell proliferation with papillary architecture. The squamous cells had pink or clear cytoplasm, intracellular bridging, irregular nuclei, and prominent nucleoli. Immunostains confirmed the squamous differentiation. Based on the histologic features and immunophenotype, a well-differentiated squamous cell carcinoma was considered one of the differential diagnoses. However, further examination of additional sections from entirely submitted lesion showed some areas with classic morphologic features of endometriosis with atypical hyperplasia. With the consideration of clinical-pathological correlations, a diagnosis of endometrioid papillary cystic borderline tumor with massive squamous differentiation was rendered and close follow-up was recommended. The patient was doing well at 4-month postoperative follow-up. Conclusion We present this case to emphasize (1) extensive squamous metaplasia arising in endometriosis can make the rendering of a definitive diagnosis challenging. (2) Primary squamous cell carcinoma of ovary is very rare. (3) Careful sampling is very important for achieving a precise pathologic diagnosis.