Diagnostic difficulties with the diagnosis of small cell carcinoma of the lung.

Small cell carcinoma of the lung (SCLC) is a well characterized form of lung cancer that is frequently already metastatic at diagnosis. Thus, patients with SCLC are usually treated with chemotherapy, and therefore emphasis has been placed on distinguishing that tumor from squamous cell carcinomas, large cell carcinomas and other pulmonary neoplasms that can more often be managed surgically. SCLC can be readily and accurately diagnosed in biopsy specimens or cytological preparations, but in selected cases, it can pose difficult diagnostic dilemmas. This review discusses selected problems encountered during the pathologic diagnosis of SCLC, including its distinction from other neuroendocrine lesions such as large cell neuroendocrine carcinoma and "carcinoid" tumors." The role of immunohistology is also considered in this context.