<b>Objectives:</b> The College of American Pathologists recommends < 60 min of ischemia time (IT) for breast cancer specimens to preserve biomarker expression. Our institution implemented a quality improvement initiative in 2019 to limit IT for the uterus to < 60 min for patients undergoing surgery for endometrial cancer (EC) in order to optimize immunohistochemistry (IHC) detection of HER2, ER, PR, and Mismatch Repair (MMR) proteins. We sought to determine patient and surgical factors that influence IT and analyze the association between prolonged IT (≥ 60 min) and biomarker expression in EC specimens. <b>Methods:</b> This is a retrospective review of patients who had a hysterectomy for EC in a comprehensive cancer center from June 2019 to February 2021. Clinical, surgical, and pathologic data were abstracted from medical records. IT was defined as the time between uterine vessel ligation to tissue fixation in formalin. We compared demographic and clinical-pathologic features for patients whose uterine specimens had IT of < 60 min to those with prolonged IT (≥ 60 min). IHC results for HER2, ER, PR, and MMR proteins were also compared between the two groups. Categorical data were compared using Chisquare or Fisher's exact test. Table 1 <b>Results:</b> Two hundred ninety-nine patients underwent hysterectomy for EC with documented IT during the study period. Most patients had endometrioid histology preoperatively (68%), had FIGO stage IA (64%), and underwent minimally invasive surgery (97%). The average length of surgery was 144 min and the average IT was 41 min. Prolonged IT occurred in 37 (12.4%) cases. Demographic factors associated with prolonged IT included age < 50 (p=0.047) and African American race (p<0.001). Uterine weight (p<0.001), need for minilaparotomy (p<0.001), additional procedures performed (p=0.006), and length of surgery (p<0.001) were associated with prolonged IT (Table 1). Day of the week, time of day, trainee involvement, and surgeon were not associated with ischemia time. IHC for HER2, ER, and PR was performed on 10%, 11%, and 10% of specimens, respectively, whereas IHC for MMR proteins was performed in 98% of cases. Though not statistically significant, there was a trend noted toward negative ER expression on IHC in specimens with prolonged IT (p=0.056). There was no association between IT and expression of HER2 (p=0.508), PR (p=0.25), and MMR proteins (p=0.143-1). <b>Conclusions:</b> Approximately 12% of EC specimens had ischemia time > 60 min. Patient factors (age < 50, race) and surgical factors (need for mini-laparotomy, additional procedures, and length of surgery) were associated with prolonged ischemia time. We suspect this is primarily due to uterine size and surgical complexity, which are not modifiable. The potential impact of IT on IHC detection of HER2, ER, PR, and MMR merits further investigation.