To determine if R-loops preferentially accumulate in MED12-mutant UFs, we performed immunohistochemical (IHC) analysis using the RNA–DNA hybrid-specific antibody S9.6 to probe tissue microarrays (TMAs) encompassing 10 patient-matched sample sets, each set comprising tissue from MM as well as one MED12-WT and one MED12-mutant UF tumor all derived from the same patient uterus. Here, MED12 is linked to neoplasm.