Chapter 40: Carcinoid Tumors and Carcinoid Syndrome

INTRODUCTION

The term “karzinoide” was first used in 1907 by pathologist Siegfried Oberndorfer to describe small intestinal tumors that resembled carcinomas on histology, but behaved less aggressively clinically.¹ In the current literature, carcinoids refer to well-differentiated, low-to-intermediate-grade neuroendocrine tumors (NETs) of the bronchopulmonary and gastrointestinal (GI) tracts.² By definition, NETs are epithelial neoplasms with both neural and endocrine differentiation, which arise from many different cell types of the neuroendocrine system.² Carcinoids represent a diverse subset of NETs, which exhibit slow growth but variable clinical presentation, growth pattern, and prognosis, depending on anatomic site and cell of origin.^2–4 This chapter describes the clinical behavior of GI carcinoids, as well as their diagnosis and management by anatomic site. It concludes with a brief description of metastatic carcinoid and carcinoid syndrome, a rare but potentially life-threatening presentation.

EPIDEMIOLOGY

GI carcinoids account for 0.5% of all newly diagnosed cancers and 71% of all NETs.⁵ Several large population studies have been conducted to document the incidence of GI carcinoids, their distribution across anatomic sites, and trends in incidence and outcomes over time, based on data from the national U.S. Surveillance, Epidemiology, and End Results (SEER) registry.^5–7 In one series of 11,427 patients with NETs reported to SEER between 1973 and 1997, the average age at diagnosis was 61 years, and cases were distributed evenly across gender.⁶ The majority of NETs arose in the GI tract (55%), followed by the bronchopulmonary tract (30%), pancreas (2%), and other rare sites including, in decreasing order, gynecologic, biliary, head and neck, and genitourinary systems.⁶ Among GI carcinoids, the small intestine was the most common site (45%, predominantly ileum), followed by rectum (20%), appendix (17%), colon (11%), then stomach (7%) (Fig. 40-1).⁶ Notably, pancreatic NETs were considered separately from GI carcinoids in this study. A more recent SEER-based series of 25,531 patients with histologically confirmed GI carcinoid tumors demonstrated similar findings, with 38% of cases arising in the small intestine, 34% in the rectum, 16% in the colon, and 11% in the stomach.⁵ Appendiceal tumors were not considered separately in this latter analysis.

The incidence of NETs has increased over the past 4 decades, with one study showing an increase of approximately 0.85 to 3.84 per 100,000 between 1973 and 1997.⁶ A more recent series estimates the annual incidence of GI carcinoid tumors to be 5 per 100,000,⁷ with the largest increases noted in localized tumors and those of the small intestine, rectum, and stomach.⁵ More widespread use of axial ...