<p>Cancer is a life-threatening illness that, beyond its physical consequences, can lead to significant psychological outcomes, including symptoms of post-traumatic stress disorder (PTSD). While core belief disruption has been linked to PTSD, the pathways underlying this relationship remain underexplored. This study aimed to examine the association between disruptions in core beliefs and PTSD symptoms in cancer patients, with a particular focus on the mediating role of intrusion and the moderating role of avoidance behavior. A total of 204 patients receiving oncology treatment participated in the study. Data were collected using the Personal Information Form, the Core Beliefs Scale, and the Impact of Events Scale-Revised. PROCESS macro for SPSS was used for the analysis: Model 4 for simple mediation and Model 5 for moderated mediation. Findings revealed that disruptions in core beliefs were significantly associated with both intrusion and hyperarousal symptoms (<i>p</i> &lt; 0.01<b>)</b>. Moreover, intrusion was found to fully mediate the relationship between core belief disruptions and hyperarousal. Avoidance behavior moderated this mediating relationship, such that the direct effect of belief disruption on hyperarousal was significant at low and high levels of avoidance, but not at moderate levels. These findings underscore the importance of addressing both cognitive disruptions and avoidance behaviors in trauma-informed interventions for cancer patients. Accordingly, the development of structured, personalized psychoeducational and therapeutic support programs is recommended to enhance psychological resilience and improve the overall quality of life in cancer survivors.</p>