Mass-like extragonadal endometriosis associated malignant transformation in the pelvis: A rare case report

BACKGROUND: Endometriosis affects approximately 10% of reproductive-age women, however, endometriosis associated malignant transformation is rare and is often report as a rare case. CASE SUMMARY: Herein, we report of a 49-year-old female patient who suffered from severe left lower abdominal pain and imaging examination revealed an irregular mass in the left iliac fossa. Histopathological examination revealed main undifferentiated adenocarcinoma with a few typical endometrial epithelial and stromal tissues in the adjacent area. Combined with the immunohistochemical staining and the negative intra- or postoperative results from exploratory laparotomy, gastroscopy, enteroscopy and positron emission tomography, the tumor was considered to be derived from endometriosis. The patient underwent hysterectomy, bilateral salpingectomy, bilateral ovariectomy, and multipoint biopsy of the pelvic peritoneum. Subsequent radiotherapy and chemotherapy were performed. The patient recovered well post-operation and there was no evidence of recurrence after 10 mo of follow-up via computed tomography and magnetic resonance imaging. CONCLUSION: This case highlights a rare presentation of mass-like extragonadal endometriosis associated malignant transformation in the pelvis. Endometriosis associated malignant transformation is rare and difficult to diagnose in clinical settings, with diagnoses depending on pathological results and the exclusion of metastasis from other organs. Fortunately, patients are often diagnosed at younger ages, as well as at early stages; thus they generally have relatively favorable prognoses.