Pulmonary neuroendocrine/carcinoid tumors

Abstract

Neuroendocrine tumors are a unique malignant neoplasm that can arise from the respiratory tree. Although well-differentiated bronchial neuroendocrine tumors (also called carcinoid tumors) are reported to account for approximately 25% of all neuroendocrine tumors, they represent only 1% to 2% of all lung cancers. The epidemiology, clinical behavior, and treatment of neuroendocrine carcinoid tumors differ significantly from other lung malignancies. In this article, the recent data regarding these tumors were reviewed with attention to the treatment modalities used. Although conventional cytotoxic therapy has not been reported to demonstrate much promise in this entity over the past 4 decades, newer molecular targeted agents including those that targeted angiogenesis and the mammalian target of rapamycin (mTOR) Well-differentiated neuroendocrine, or carcinoid, tumors are a unique class of malignancies capable of producing hormones identical to those from the nervous system. Although the first carcinoid tumor described was in the ileum, neuroendocrine malignancies are a family of malignancies found throughout the body. Tumors of the bronchial tree in particular account for approximately 25% of all well-differentiated neuroendocrine tumors (Table 1). [1][2][3] However, compared with other malignancies of the bronchoalveolar tree, these well-differentiated neuroendocrine tumors are rare, accounting for only 1% of all lung cancers. 3 The pathologic spectrum of neuroendocrine malignancies ranges from low-grade carcinoid to aggressive small cell lung cancer. The low-grade and intermediate-grade neuroendocrine malignancies, also known as typical and atypical carcinoid, will be the focus of this review. The distinct features of this malignancy include its pathologic characteristics, clinical behavior, epidemiology, prognosis, and treatment.

Neuroendocrine Tumors of the Lung

“…The differential diagnosis includes tumorlets. DIPNECHS are considered as preneoplastic lesions (WHO 2004) due to the possible progression to carcinoids [1][2][3]8,15].…”

“…Clinically, approximately 20%-40% of patients with typical or atypical carcinoids are nonsmokers, whereas nearly all patients with SCLC (95% of all SCLC arise in the bronchial system) and LCNEC are heavy cigarette smokers [2]. Lung tumors include 1-2.0% carcinoids (AC ~ 0.1-0.2%), 3.0% LCNEC, 15-20.0% SCLC and 75-80% non-neuroendocrine carcinomas [1][2][3]8,18]. Patients with inherited autosomal-dominant syndrome of multiple endocrine neoplasia type I (MEN I) and other hereditary histories show a higher incidence of malignant neuroendocrine lesions [19].…”

“…Synthetic analogues bind mainly to SSTR 2 , and much less to SSTR 5 . Those synthetic analogues of the peptide hormone somatostatin, octreotide and lanreotide (also in case of inoperable carcinoids), are being the most widely used ones in controlling carcinoid syndrome with metastatic well-differentiated neuroendocrine tumors and are still debated [3,19,22]. Reghi and colleagues compared the immunohistochemical expression pattern of SSTR versus SSTR scintigraphy.…”

“…This classification of NETs is based on macroscopic, microscopic and immunohistochemical features. Therefore, the mitotic activity (mitosis/2 mm 2 = (10 high power fields)) as well as the rosette-like structure, palisading, trabecular pattern, organoid nesting and the proportion of necrosis are common characteristics of pulmonary neuroendocrine tumors [1,3,6,10,13]. Neurosecretory granules can be demonstrated by electronmicroscopy.…”

“…Neurosecretory granules can be demonstrated by electronmicroscopy. Table 1 summarizes additional important macroscopical, histological and cytological features of pulmonary neuroendocrine tumors [1,3,6,8,10,13]. Most common disagreements exist between LCNEC versus SCLC, typical versus atypical carcinoid and atypical carcinoid versus LCNEC [6,8].…”