Background/Aim: Uterine leiomyoma, also known as fibroids, is the most common benign neoplasm of the female genital tract. Leiomyoma, including its subtypes, is the most common uterine tumor. The subtypes account for approximately 10% of leiomyomas. Intravenous leiomyomatosis, a uterine leiomyoma subtype, is an intravascular growth of benign smooth muscle cells, occasionally with pelvic or extrapelvic extension. Uterine leiomyosarcoma, a malignant tumor, tends to metastasize hematogenously, and distant metastasis to the lungs and liver is common. Therefore, this intravenous leiomyomatosis’ oncological features resemble those of the malignant tumor uterine leiomyosarcoma. Cancer stem cells migrate to distant organs via intravascular infiltration, leading to micrometastases. Materials and Methods: We examined the oncological properties of intravenous leiomyomatosis using molecular pathological techniques on tissue excised from patients with uterine leiomyoma. Result: CD44-positive mesenchymal tumor stem-like cells were detected in both intravenous leiomyomatosis and uterine leiomyosarcoma. The oncological nature of intravenous leiomyomatosis was found to be similar to the oncological properties of uterine leiomyosarcoma. However, in intravenous leiomyomatosis, Cyclin E and Ki-67-positive cells were rare, and no pathological findings suspected to be malignant were observed. Conclusion: It is expected that establishing a treatment method targeting cancer stem cells will lead to the treatment of malignant tumors with a low risk of recurrence and metastasis.