Incidence of psychiatric illness in patients with neuroendocrine tumors: a comparative population-based analysis.PURPOSE
 Diversion of tryptophan to tumoral hormonal production has been suggested to result in psychiatric illnesses in neuroendocrine tumors (NET).  We measured the occurrence of psychiatric illness after NET diagnosis and compare it to colon cancer (CC).


 We conducted a population-based retrospective cohort study.  Adults with NET were matched 1:1 to CC (2000-2019).  Psychiatric illness was defined by mental health diagnoses and mental health care use after a cancer diagnosis, categorized as severe, other, and none.  Cumulative incidence functions accounted for death as a competing risk.


 RESULTS
 A total of 11,223 NETs were matched to CC controls.  Five-year cumulative incidences of severe psychiatric illness for NETs vs. CC was 7.7% (95%CI 7.2-8.2%) vs 7.6% (95%CI 7.2-8.2%) (p = 0.50), and that of other psychiatric illness was 32.9% (95%CI 32.0-33.9%) vs 31.6% (95%CI 30.8-32.6%) (p = 0.005).  In small bowel and lung NETs, 5-year cumulative incidences of severe (8.1% [95%CI 7.3-8.9%] vs. 7.0% [95%CI 6.3-7.8%]; p = 0.01) and other psychiatric illness (34.7% [95%CI 33.3-36.1%] vs. 31.1% [95%CI 29.7-32.5%]; p < 0.01) were higher than for matched CC.  The same was observed for serotonin-producing NETs for both severe (7.9% [95%CI 6.5-9.4%] vs. 6.8% [95%CI 5.5-8.2%]; p = 0.02) and other psychiatric illness (35.4% [95%CI 32.8-38.1%] vs. 31.9% [95%CI 29.3-34.4%]; p = 0.02).


 In all NETs, there was no difference observed in the incidence of psychiatric illness compared to CC.  For sub-groups of small bowel and lung NETs and of serotonin-producing NETs, the incidence of psychiatric illness was higher than for CC.  These data suggest a signal towards a relationship between those sub-groups of NETs and psychiatric illness.
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