AIM To discover unknown factors associated with carcinoid syndrome(CS) with the goal of earlier diagnosis of CS.METHODS In this retrospective case-control study using United States administrative claims, patients(≥ 18 years) newly-diagnosed with gastrointestinal neuroendocrine tumors(GI NETs) without CS(controls) were exactly matched to patients with CS(cases) based on NET diagnosis date at a 3-to-1 ratio. Study index date was first CS diagnosis(controls: same distance from NET diagnosis as cases). The most observed conditions, excluding CS-associated symptoms/diagnoses, during the year before index date were assessed. Forwardstepwise logistic regression models were used to derive predictors, and were validation within another claims database. RESULTS In the development database, 1004 patients with GI NETs were identified; 251(25%) had CS and 753(75%) were controls. In the validation database, 724 patients with GI NETs were identified; 181(25%) had CS and 543(75%) were controls. A total of 33 common diagnoses(excluding conditions already known to be associated with CS) in the development database were entered in forward step-wise logistic regression models. In the final, validated logistic regression model, three factors prior to CS diagnosis were found consistently associated with higher risks for CS, including liver disorder [odds ratio(95%CI): 3.38(2.07-5.51)], enlargement of lymph nodes [2.13(1.10-4.11)], and abdominal mass [3.79(1.87-7.69)].CONCLUSION GI NET patients with CS were 2-4 times as likely to have preexisting diagnoses(i.e., liver disorder, enlarged lymph nodes, abdominal mass) than non-CS patients. AIM To discover unknown factors associated with carcinoid syndrome (CS) with the goal of earlier diagnosis of CS.METHODS In this retrospective case-control study using United States administrative claims, patients (≥ 18 years) newly-diagnosed with gastrointestinal neuroendocrine tumors NETs) without CS (controls) were exactly matched to patients with CS (cases) based on NET diagnosis date at a 3-to-1 ratio. Study index date was first CS diagnosis (controls: same distance from NET diagnosis as cases). The most observed conditions, excluding CS-associated symptoms / diagnoses, during the year before index date were assessed. Forwardstepwise logistic regression models were used to derive predictors, and were validation within another claims database. RESULTS In the development database, 1004 patients with GI In the validation database, 724 patients with GI NETs were identified; 181 (25%) had CS and 543 (75%) were controls. A to in the final, validated logistic regression model, three factors prior to CS diagnosis were found consistently associated with higher risks for CS, including liver disorder [odds ratio (95% CI: 3.38 (2.07-5.51)], enlargement of lymph nodes [2.13 (1.10-4.11)], and abdominal mass [3.79 (1.87-7.69)] .CONCLUSION GI NET patients with CS were 2-4 times as likely to have preexisting diagnoses (ie, liver disorder, enlarged lymph nodes, abdominal mass) than non-CS patients.