Based on above discussions, differential diagnoses are low grade endometrial stromal tumor versus adenosarcoma with sarcomatous overgrowth. I guess the puzzle will be the epithelial component which is cystic and benign appearing. If I bet, I favor endometrial stromal sarcoma based on the followiing thinking process:

1) Most adenosarcoma with sarcomatous overgrowth in our hands are high grade sarcoma with ovbious nulcear atypia and active mitosis. The prognosis is usually just like MMMT. This case is very indolent and low grade looking. Therefore, it is less likely to be sarcomatous overgrow seen in adenosarcoma, rather a low grade endometrial stromal tumor is favored.

2) IHC stains provided is not useful in differentiating these two entities, although it is profile perfectly match with low grade endometrial stromal tumor of the ovary.

3) Now we have to deal with epithelial component. If epithelial cyst is very local, my bet is that these are paratubal serous cyst trapped in this EM stromal tumor.

 现提供免疫组化结果：

肿瘤细胞CD10（+）、SMA（+）、ER（+）、PR（+）。腺上皮ER（+）、PR（+）。

间叶成分看上去像内膜间质肉瘤，平滑肌肉瘤也不能完全排除，需要看看免疫组化的CD10和SMA、DES的阳性程度和比例。不知腺上皮的成分有多少？在肿瘤中的分布如何？

这是个有趣的例子。