Low-grade endometrial stromal sarcoma with sex cord-like differentiation metastatic to the thoracic spines

We report a case of monostotic low-grade stromal sarcoma (ESS) with sex cord-like elements metastatic to the thoracic spines, which to the best of our knowledge has not previously been documented. A 48-year-old female who had undergone total abdominal hysterectomy for low-grade endometrial stromal sarcoma 7 years previously presented with insidious onset of severe back pain of 2 months' duration. Magnetic resonance image (MRI) showed involvement of the eleventh and twelfth thoracic vertebral bodies. Decompression at the level of T10-12 was performed. Histologically, the laminae of thoracic vertebrae 11 and 12 were replaced by sheets of ovoid cells with plump nuclei intermixed with anastomosing trabeculae, cords and small nests, reminiscent of a sex-cord stromal tumor pattern. The tumor cells showed diffuse nuclear immunostaining for estrogen receptors (ER) and progesterone receptors (PR), as well as membranous immunostaining for CD10. The immunostaining for smooth muscle actin was focal and sparse. These findings confirmed the diagnosis of metastatic low-grade ESS with sex cord-like differentiation. Low-grade ESS with sex cord-like differentiation is an uncommon tumor which rarely metastasizes to the bone, and use of a panel of ER, PR, CD10, actin, cytokeratin and inhibin immunostains is essential to establish the diagnosis.