RESUMEN
(1) Introduction: Cancer diagnosis has been related to depression, anxiety, and distress, as well as to post-traumatic growth (PTG). One of the mediating variables for emotional response is thought style (rumination, cognitive avoidance, and cognitive engagement). (2) Aim: To identify the relationship between thought style and emotional responses to cancer. A secondary aim was to identify the relationship between emotional responses and inflammatory immunological biomarkers. (3) Method: A total of 115 patients with cancer were included in the study. Before initiating cancer treatment, patients were assessed using the Hospital Anxiety and Depression Scale (HADS), distress thermometer, and Post-Traumatic Growth Inventory (PTGI). Patients provided their most recent blood biometry. (4) Results: Rumination correlated with anxiety, depression, and distress. Cognitive avoidance correlated with PTG (-0.240) and distress (-0.209). Cognitive engagement correlated with PTG (0.393). Regarding thought style and biomarkers, a negative correlation was observed for absolute neutrophils with cognitive avoidance (-0.271) and rumination (0.305). Regarding biomarkers and emotional responses, there was a negative correlation between PTG and absolute lymphocytes (-0.291). There was also a correlation between PTG and neutrophils (0.357) and neutrophil-to-lymphocyte ratio (NLR) (0.295). (5) Conclusions: Thought style is related to the emotional response to a cancer diagnosis; rumination is related to depression, distress, and anxiety; and cognitive engagement is related to PTG. PTG is related to inflammation and immunological biomarkers.