MED12 and leiomyoma: The known leiomyoma driver alterations were observed in 40% of the tumors: MED12 mutation frequency was slightly, but not significantly, lower in mitotically active ULs (36%, 9/25) compared to conventional leiomyomas (Table 1, Fig. 1, see Additional file 5: Table S2 and Additional file 6: Table S3).