Individual personality refers to the Ego and the interpersonal sector. The Ego corresponds to consciousness and self-esteem, including the capacities for emotional self-regulation, self-control, self-evaluation, and self-direction in relation to personal goals. When neoplastic and psychiatric diseases coexist, a patient’s quality of life is significantly impacted. While there are somatic differences in disease progression, how the illness is perceived and mainly experienced depends on personality traits. In this study, we administered the DECAS Personality Inventory (a Romanian-validated instrument based on the Five-Factor model of personality) to a group of 121 patients diagnosed with breast cancer to explore the relationships among their personality traits. Descriptive statistics revealed that the mean T scores for openness, extroversion, and emotional stability were low, while the scores for conscientiousness and agreeableness were at an average level. Our findings suggest that, in the studied group, low levels of emotional stability, extroversion, and openness were unfavorable personality dimensions that should be a primary focus of therapeutic strategies, as they significantly affect the quality of life in patients with breast cancer.