Peritoneal endometriosis in the broad ligament presenting as a large tumor

Peritoneal endometriosis presenting as a tumor is very rare. A case of peritoneal endometriosis in the broad ligament presenting as a large tumor is reported. A 39-year-old woman had a solid and cystic tumor with many microcysts, measuring 17 x 13 x 3.5 cm, mainly located in the right posterior broad ligament. Histologically, the tumor consisted of many endometrial glands associated with various amounts of endometrial stroma. Neither the glands nor the stromal cells had cellular atypia. We diagnosed peritoneal endometriosis presenting as a tumor. Among the six cases (five previously reported cases and our case) of tumor-like endometriosis in the peritoneum, two cases (33%) had received tamoxifen therapy and four cases (67%) had cystic or solid and cystic tumor. Among them, the tumor size ranged from 3 to 17 cm in diameter, and our case was the largest. In conclusion, this case is rare, but it is important for pathologists to be aware of the phenomenon (that extensive peritoneal endometriosis produces a large tumor) in the histological diagnosis of a tumor in the peritoneum.