GREB1 ‐rearranged uterine tumour shares a common DNA methylation signature with ESR1 ‐rearranged UTROSCT

BACKGROUND AND OBJECTIVES: GREB1-rearranged uterine tumours encompass a group of uterine mesenchymal tumours with varied histologic appearances. The fusion partners to GREB1 include NCOA1-3, SS18 and NR4A3. Given that some GREB1-rearranged uterine tumours exhibit histologic features of uterine tumours resembling ovarian sex cord tumour (UTROSCT), there is a general belief that GREB1-rearranged uterine mesenchymal tumours are part of the UTROSCT family. METHODS: In this study, we applied global DNA methylation and copy number analyses to a series of 10 GREB1-rearranged uterine tumours and 21 classic UTROSCTs (7 of which were molecularly confirmed to harbour ESR1::NCOA2/3 fusions). RESULTS: We found that GREB1-rearranged uterine tumors show an overlap in their global methylation profiles with UTROSCT, including ESR1::NCOA2/3 positive cases. Together, these tumours form a DNA methylation cluster separate from uterine smooth muscle tumours (leiomyomas and leiomyosarcomas), endometrial stromal sarcomas (low-grade and high-grade), embryonal rhabdomyosarcoma and SMARCA4-deficient uterine sarcomas. However, despite their epigenetic similarity, there were two notable differences. First, GREB1-rearranged uterine tumours as a group displayed a greater degree of genomic complexity with more extensive copy number alterations than conventional UTROSCTs, including those harbouring ESR1::NCOA2/3. Second, GREB1-rearranged uterine tumours frequently lacked overt sex cord morphology: while all 7 ESR1::NCOA2/3 UTROSCTs demonstrated corded, nested, trabecular and/or tubular/sertoliform patterns, only 1 GREB1-rearranged uterine tumour displayed a prominent trabecular pattern, with the remaining cases showing exclusively or predominantly diffuse/solid growth. CONCLUSIONS: Overall, our findings confirm that GREB1-rearranged uterine tumours are part of the UTROSCT spectrum, though they frequently exhibit a more diffuse growth pattern and a higher degree of genomic instability.