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.