Objective:To investigate the association between cancer fatalism and optimistic attitudes among colorectal cancer patients, and how the above linkage is moderated by the involvement of patients′ opinions, the family members′ opinions and the physicians′ opinions in treatment decision-making.Methods:A cross-sectional survey was conducted on 64 patients diagnosed with colorectal cancer and awaiting radical colorectal cancer surgery in the Department of General Surgery of Beijing Friendship Hospital Affiliated to Capital Medical University, from January 2021 to December 2021. There were 38 males and 26 females, aged (61.2±13.0) years from 30 to 84 years. Cancer fatalism, optimism attitudes, and the involvement of patients′ opinions, the family members′ opinions and the physicians′ opinions in treatment decision-making were assessed. The patients′ cancer fatalism beliefs were measured by the " Chance" subscale of the Form C of the Multidimensional Health Locus of Control (MHLC-C), optimism attitudes were assessed by the Chinese version of the revised Life Orientation Test (CLOT-R), and the influence of patients′, family members′, and physicians′ opinions in the medical decision-making process was measured by a self-designed single factor scale. Measurement data of normal distribution were expressed as mean±standard deviation ( ± s). Measurement data of skewed distribution were expressed as M( Q1, Q3). Spearman correlation analysis and Chi-square test was used to examine the association between the main outcome variable (patients′ optimistic attitudes) and demographic and clinical characteristics. Interaction was examined by hierarchical linear regression analysis combined with simple slope tests. Results:Cancer fatalism was negatively associated with patients′ optimistic attitudes ( r=-0.35, P<0.01). Optimistic attitude of patients was significantly and negatively correlated with the influence of family members′ opinions on medical decision-making ( r=-0.25, P<0.05). There were significant positive correlations between the influence of patients′ and family members′ opinions ( r=0.50, P<0.01), family members′ and physicians′ opinions ( r=0.67, P<0.01), and physicians′ and patients′ opinions ( r=0.38, P<0.01) in medical decision making. Hierarchical linear regression analysis showed a negative association between cancer fatalism and optimism ( β=-0.32, P=0.01). This association was further moderated by the involvement of family members′ opinions ( β=-0.56, P<0.01) and the involvement of physicians′ opinions ( β=-0.36, P=0.04) in medical decision-making. Simple slope tests revealed that the negative impact of fatalistic attitudes on patients′ optimism attitudes may be potentiated when family members′ opinions have high influence on medical decision-making, while the negative impact may be buffered to some extent when physicians′ opinions have high influence on medical decision-making. Conclusions:Cancer fatalism had a negative effect on patients′ optimism. The high influence of physicians in treatment decision-making buffered the negative effect of cancer fatalism on optimism; the high influence of family members in treatment decision-making potentiated the negative effect of cancer fatalism on optimism. In the process of doctor-patient communication and shared decision-making, for patients with strong fatalistic attitudes, consideration should be given to appropriately increasing direct informational communication between physicians and patients and reducing excessive family intervention in medical decision-making, so as to enhance patients′ autonomy for treatment, promote optimism, and reduce the negative effects of cancer fatalism.