Neuroendocrine carcinomas of the lung

Abstract

N EUROENDOCRINE carcinomas of the lung are tumors related to the Kulchitsky cell, a neuroendocrine cell normally present in the bronchial mucosa.lV2 These tumors account for approximately 25% of all lung tumors and include three subtypes: classic carcinoid, atypical carcinoid, and small cell carcinoma. These three different subtypes share many common morphologic and biochemical features, but represent a spectrum of aggressiveness with some overlap of clinical, radiologic, and pathologic features.‘V3 A more extensive discussion of the pathology of these tumors is given in the article by Pietra in this issue. Classification into three subtypes is important because their treatment and prognosis are different.4 At one end of the spectrum is the carcinoid tumor, a low-grade carcinoma with low incidence of metastasis and good prognosis following surgical resection. At the other end of the spectrum is the small cell carcinoma, an extremely malignant tumor that metastasizes early in its course and is usually not amenable to surgical resection. The treatment consists of chemotherapy and radiotherapy. Atypical carcinoids are tumors of intermediate malignant potential and prognosis. They are usually treated by lobectomy or pneumonectomy with or without adjuvant chemotherapy and radiotherapy. Because of the differences in treatment among these tumors, accurate preoperative diagnosis is critical. However, because of the overlap between the three subtypes and their similar cytologic features, preoperative differential diagnosis is difficult and often misleading. Cytologic specimens obtained by sputum, bronchoscopy, or fine-needle aspiration biopsy are usually able to suggest the diagnosis of neuroendocrine carcinoma, but there is unavoidable error in distin-