A mass excised from the uterus of a 30-year-old female shows a single lesion with areas of necrosis and hemorrhage. What is this mass most likely?

The mass described in the scenario is most likely a leiomyosarcoma, which is a malignant tumor of smooth muscle origin. The key characteristics supporting this diagnosis include the presence of a single lesion exhibiting areas of necrosis and hemorrhage.

Leiomyosarcomas are known to be aggressive tumors that can arise in the uterus and often present with such features. They are distinct from leiomyomas, which are benign smooth muscle tumors that generally do not demonstrate necrosis or hemorrhage and have a more well-defined and circumscribed appearance. Endometrial hyperplasia refers to an abnormal increase in the endometrial lining, which typically does not present as a mass and is less likely to be associated with necrosis. Endometrial carcinoma, while it can be malignant and show some necrosis, usually presents differently and may involve abnormal bleeding rather than being characterized by a single mass with such distinct necrotic features.

In summary, the presence of necrosis and hemorrhage, along with the theater of a single lesion, strongly points toward leiomyosarcoma as the most probable diagnosis in this clinical scenario.