ZC3H7B-BCOR high-grade endometrial stromal sarcoma may present as myoma nascens with cytoplasmic signet ring cell change.

We report on 51-year-old woman who presented with brown discharge and postcoital bleeding due to myoma nascens-like polypoid mass distending cervical canal. Histologically, the tumor consisted of high-grade spindle cell component with up to 15 mitotic figures per 10 HPF and also low-grade leiomyoma-like areas with focal myxoid change and so far undescribed cytoplasmic signet ring cell change. Immunohistochemically Desmin, actin, and h-caldesmon were negative. Conversely, BCOR positive expression was coupled with Cyclin D1 positivity and was antibody clone dependent. The molecular NGS and FISH study identified reciprocal fusion gene ZC3H7B-BCOR. In conclusion, these findings further support the idea of routine reflex molecular testing of uterine mesenchymal tumors with unusual clinical presentation or in case malignancy is suspected. Lastly, we suggest ZC3H7B-BCOR rearranged high-grade endometrial stromal sarcoma might be considered as a tumor suitable for BCL6-targeted treatment.