Abstract Objective: To evaluate the prevalence of financial toxicity in women diagnosed with advanced/recurrent endometrial cancer and describe characteristics and qualitative aspects of financial stressors in this population. Methods: Women diagnosed with advanced/recurrent endometrial cancer at an urban academic center were invited to participate in a mixed-methods study to describe quality-of-life (QOL) and financial toxicity. Participants completed surveys including the EuroQOL-5D-5 (QOL), financial toxicity tool (COmprehensive Score for Financial Toxicity (COST)) and completed an interview inquiring about financial stressors. Descriptive statistics were performed, and interviews were transcribed and analyzed using Atlas.ti to identify themes. Results: Eighty-four women participated in the study reflecting a 90% response rate. Participants were a median age of 67.0 years and 6 (7%) self-identified as Hispanic. Most participants self-identified as White (41, 49%), followed by Black (35, 42%), and multiracial (8, 10%). Forty (49%) participants had advanced stage cancer while 42 (52%) had recurrent cancer, with endometrioid adenocarcinoma (41,50%) represented as the most common histology followed by serous carcinoma (18, 22%), carcinosarcoma (11, 13%), the remaining clear cell carcinoma/mixed/undifferentiated (14, 17%). The median financial toxicity score of the population was 28.0 (IQR: 21-35) out of 44.0, with 38.1% of participants reporting moderate financial toxicity (COST <26) and 8.3% reporting severe financial toxicity (COST <14). Lower financial toxicity scores (indicating poor financial wellness) were associated with younger age (<65yo: 24.0 vs. >65yo: 32.0; p<0.01), Black and multiracial participants compared to white participants (Black: 26.0, multiracial: 16.5, white: 33.0; p<0.05), Hispanic ethnicity (13.5 vs. 30.0; p<0.001), single marital status (26.0 vs. 33.0; p<0.05), and lower education (Less than college: 24.1 vs. college and above: 30.0; p<0.05). On multivariate linear regression, financial toxicity scores were associated positively with older age (B= 6.5, p<0.01) and non-single marital status (B=4.8, p<0.05) but were negatively associated with Hispanic ethnicity (B= -11.4, p<0.05). The median QOL score (health utility score) of the population was 0.80 (IQR: 0.71- 0.85) and this score was positively correlated with better financial wellness (higher financial toxicity score) (R= 0.3, p<0.05). Qualitative analysis of participant interviews found that participants experiencing financial toxicity reported themes of “forced retirement” and “forced work interruptions” (9, 11%) while those with financial wellness praised “quality insurance coverage” (19, 23%). Conclusion: Patients with advanced/recurrent endometrial cancer experience a high rate of financial toxicity. Although limited by sample size, financial toxicity was found to be significantly worse in younger, single, and Hispanic women. Further work to study this at-needs population should be done to identify causes and develop solutions to assist patients with financial stressors. Citation Format: Sarah A. Ackroyd, Gini Fleming, Nada Attia, Cheska Zoleta, Nita K. Lee. The cause behind the COST – exploring qualitative and quantitative aspects of financial toxicity in women diagnosed with advanced/recurrent endometrial cancer [abstract]. In: Proceedings of the AACR Special Conference on Endometrial Cancer: Transforming Care through Science; 2023 Nov 16-18; Boston, Massachusetts. Philadelphia (PA): AACR; Clin Cancer Res 2024;30(5_Suppl):Abstract nr A005.