Carcinoids of unknown origin: Comparative analysis with foregut, midgut, and hindgut carcinoids

Background. Carcinoids are rare neuroendocrine tumors typically arising in the gastrointestinal tract. A significant percentage of these tumors presen t as metastatic disease of unknown primary site. The aim of this study was to better define the functional and clinical characteristics of carcinoids of unknown primary (CUP) site. Methods, This study examines the hormonal activity clinical characteristics , and survival of 434 patients with carcinoids originating in the foregut, midgut, hindgut, or unknown location. The 143 patients with CUP were compar ed with the other groups with regard to presenting characteristics, diagnos tic tests and therapeutic modalities used, hormonal activity, and survival. Results. The hormone levels (urinary 5-hydroxyindoleacetic acid and seroton in, serum and platelet serotonin) of CUP were not significantly different f rom midgut carcinoids with metastatic disease. Although survival with CUP w as shorter than with carcinoids with identified primaries (10-year survival s of 22 % vs 62 %, 50 %, and 48 % for foregut, midgut, and hindgut, respect ively), the survival curve for CUP was quite similar to that of patients wi th midgut carcinoids with distant disease (10-year survival of 22% vs 28%). Conclusions. CUP are similar to midgut carcinoids presenting with metastati c disease with regard to hormone production and survival. Like other carcin oids, CUP can be an indolent disease process with gradual progression over decades.