Abstract Background: According to the statistics from 2013 to 2017 at the national cancer institute, more than 30% of breast cancer patients are under the age of 54, and their children are mostly minors. Diagnosis and treatment of breast cancer have a substantial impact on the patients themselves and as caregivers, resulting in both depression and parenting stress. Although there are previous studies investigating the parenting stress in patients with cancer, the factors affecting the parenting stress and depression in young women with breast cancer still remain inconclusive. Herein, we aimed to determine the parenting stress and depression of women diagnosed with breast cancer, and to identify the risk factors. Methods: A cross-sectional survey was conducted among 700 patients with breast cancer who visited the breast surgery outpatient clinic in a tertiary hospital from June 2020 to April2021. The study subjects were between 20 and 45 years old at the time of cancer diagnosis. Two-hundred patients without children were included for comparison regarding depression. The center for epidemiologic studies depression scale (CES-D) was used for evaluating depression in all subjects. Five-hundred patients with children also fill out the questionnaires including parenting stress index/short Form (PSI-SF), Child behavior checklist (CBCL), Junior temperament and character inventory (JTCI), and Children’s sleep habits questionnaire(CSHQ).Results: The risk of depression was significantly higher in patients having children (odds ratio [OR], 2.261; 95% confidential interval [CI],1.009-5.063; p=0.047) and who received gonadotropin-releasing hormone agonist (GnRH)treatment (OR 1.667; 95% CI, 1.142-2.433 p=0.008). Meanwhile, longer disease duration was associated with lower risk of depression (OR 0.852; 95% CI, 0.756-0.959 p=0.008). In regards to parenting stress, clinical factors related to breast cancer such as stage and type of treatment did not show significant association. However, children factors including the age (≥ 6 years old), specific behavioral patterns, temperature, and sleep habits reported significant impact on parenting stress. The significant correlation was noted between depression score and parenting stress score (β coefficient =0.557; p<0.0001).Conclusion: In patients with breast cancer, having children, shorter duration from the diagnosis, and treatment with GnRH was associated with higher risk of depression. Among the patients having children, the factors related to children had a significant impact on parenting stress, whereas no association was noted among clinical factors related to breast cancer. Citation Format: Yungil Shin, Harin Kim, Seonok Kim, Sae Byul Lee, Jisun Kim, Il Yong Chung, Beom Seok Ko, Jong Won Lee, Byung Ho Son, Sei Hyun Ahn, Hyo-won Kim, Hee Jeong Kim. Factors affecting the parentingstressand depressioninyoung women with breast cancer [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P4-09-03.