Imaging of Small-Cell Lung Cancer Abid Irshad, MD, a and James G. Ravenel, MD a Small-cell lung cancer (SCLC) is an aggressive pul- monary neoplasm that is known to have a distinct pathological behavior, pattern of spread, prognosis, and response to treatment as compared with the other types of lung cancers. Consequently, it is considered as a separate clinical entity from adeno-, squamous- cell, and large-cell carcinomas commonly grouped together as non-small-cell lung cancers (NSCLC). Most small-cell lung cancers arise from the proximal airways 1,2 and demonstrate rapid intra- and extra- bronchial growth. Due to its aggressive behavior, SCLC tends to metastasize early in the course of disease, both to regional lymph nodes and to distant sites. Because the primary lesion is often impercepti- ble, the imaging presentation is that of a mediastinal mass. 3 Rarely, SCLC may present as a solitary pul- monary nodule, without evidence of distant spread of disease. Epidemiology and Prognosis SCLC accounts for approximately 20% of all primary lung cancers and occurs almost exclusively in cigarette smokers. 3,4 The incidence is higher in males, but is rising in females. There is slightly higher incidence in whites as compared with Afro-Americans. 5 Radon exposure and exposure to the chemical agent chloro- methyl ether have also been associated with SCLC. In comparison to NSCLC, SCLC occurs in a slightly younger age group. Two staging systems have been developed for SCLC. The simplest and more common way is to classify the disease as “limited” or “extensive” disease according to the criteria proposed by the “Veteran Administration Lung Cancer Study Group.” 6 Accord- ing to this, limited disease is considered to be present when the tumor mass is confined to one hemithorax, mediastinum, and ipsilateral supraclavicular node and can be encompassed by a single “tolerable” radiation port. Any metastatic disease outside the thorax or disease that cannot be encompassed by a single radi- ation port is defined as extensive disease. SCLC may also be staged by the TNM classification system. Although usually reserved for non-small-cell lung cancer, this classification can be used in rare instances where SCLC presents as a solitary pulmonary nodule and surgery is contemplated. 6 Overall, the prognosis of SCLC is poor with a median survival of 14 to 16 months for limited disease and 8 to 11 months for extensive disease. Only about 4% patients are alive and disease-free 5 years after diagnosis. 7 The short-term prognosis is slightly better for limited disease 8 with a 2-year survival of about 10%, compared with 2% survival rate for extensive disease. Up to two-thirds of SCLC patients will have extensive disease at presentation. The subgroup of patients with only brain metastases does better than other forms of extensive disease and has similar prognosis as limited disease. 9 There is an increased incidence of a second malignancy in the long-term survivors of SCLC, 10 although smoking cessation may decrease the risk of a second lung cancer. 11 Limited disease is usually treated with multi-mo- dality therapy, ie, radiation and chemotherapy. Exten- sive disease is usually treated with chemotherapy alone with radiation reserved for palliation of pain or bronchial obstruction. 4 Treatment frequently results in short remission; however, local recurrence and meta- static disease are the rule. Patients are rarely surgical candidates even with a solitary pulmonary nodule due to the presumed presence of micrometastases, al- though in some centers, surgery and perioperative chemotherapy for pathologic T1N0 or N1 disease may be performed. 12 From the Department of Radiology, Medical University of South Carolina, Charleston, SC. Reprint requests: Abid Irshad, MD, Department of Radiology, Medical University of South Carolina, Box 250322, 169 Ashley Ave., Charleston, SC 29424. E-mail: irshada@musc.edu. Curr Probl Diagn Radiol 2004;33:200-11. © 2004 Elsevier Inc. All rights reserved. 0363-0188/2004/$30.00 + 0 doi:10.1067/j.cpradiol.2004.06.003 200 Curr Probl Diagn Radiol, September/October 2004