A small study from 2005 showed a higher frequency of MIB-1 and a lower estrogen/progesterone receptor expression in endometrial stromal sarcomas than in endometrial stromal nodules [9], suggesting that these biomarkers will be able theoretically to distinguish between the types and thereby allow a more conservative treatment when diagnosed with a benign type. This evidence concerns the gene MIB1 and endometrioid stromal sarcoma.