Abstract Introduction: Biological aging leads to an increased risk of morbidity and mortality in patients with head and neck cancer (HNC) undergoing intensity-modulated radiotherapy (IMRT). This progression can be exacerbated by the burden of stress arising from HNC and IMRT. While stress has been linked to inflammation, the associations of biological aging measures including inflammatory markers and epigenetic age acceleration (EAA) with stress over cancer treatment remain underexplored. The purpose of this study was to examine the associations between biological aging and stress in patients with HNC receiving IMRT across four time points (i.e., pre- (T1), end of (T2), 3 months (T3), and 12 months (T4) post-IMRT). Methods: We conducted a prospective longitudinal study. Stress was assessed using the Perceived Stress Scale (PSS) across four time points along with the assessment of biological aging markers: peripheral inflammatory markers (i.e., interleukin [IL-6], IL-1β, IL-10, IL-1ra, C-reactive protein [CRP], soluble tumor necrosis factor receptor 2 [sTNFR2], and TNF-α) and EAA. EAA was calculated using DNAmPhenoAge, adjusted for chronological age. Liner mixed effects models were used to examine the associations between biological aging measures and stress across time. Results: A total of 176 patients with HNC were enrolled in the study with a mean age of 59.9±10.0 years, 72.7% male, and 77.3% non-Hispanic White. Stress scores increased from T1 to T2 (p<0.001), decreased significantly at T3 (p<0.001) which were lower than the baseline scores (T1), and then gradually decreased at T4 (p=0.029). Significant associations of CRP, IL- 1ra, and TNFR-2 with stress were identified across time (all p values <0.05), controlling for covariates (i.e., age, human papillomavirus status, chemotherapy, and surgery): elevated inflammatory markers were associated with higher levels of stress. In a separate model, higher stress scores were also associated with increased EAA controlling for the same covariates (p=0.015): an increment of 10 units in stress scores was associated with an age acceleration of 7.2 months across time. Conclusions: Findings from our study suggest that biological aging measures (inflammatory markers and EAA) are associated with stress across time in patients with HNC receiving IMRT. Clinicians and researchers may use the findings to develop personalized psychosocial interventions that reduce stress so as to deaccelerate biological aging for patients with HNC during their treatment and survivorship. Citation Format: Yufen Lin, Telisa Spikes, Deborah Bruner, Sudeshna Paul, Andrew Miller, Karen Conneely, Nabil Saba, Canhua Xiao. Associations of biological aging with perceived stress in patients with head and neck cancer: A longitudinal study [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6300.