Lung cancer is a large and exceptionally heterogeneous family of malignancies. Over 50 different histological variants are explicitly recognized within the 2004 revision of the World Health Organization (WHO) typing system ("WHO-2004"), currently the most widely used lung cancer classification scheme. Many of these entities are rare, recently described, and poorly understood. However, since different forms of malignant tumors generally exhibit diverse genetic, biological, and clinical properties — including response to treatment — accurate classification of lung cancer cases are critical to assuring that patients with lung cancer receive optimum management. Approximately 99% of lung cancers are carcinoma, a term that indicates that the malignant neoplasm is composed of, or descended from, cells of epithelial lineage (i.e. derived from embryonic endoderm, as is the case in lung carcinomas, or from ectoderm), and/or that the malignant cells exhibit tissue architectural, cytological, or molecular features characteristically found in epithelial cells. Under WHO-2004, lung carcinomas are divided into 8 major taxa: * Squamous cell carcinoma *<unk>  cell carcinoma * Adenocarcinoma * Large cell carcinoma * Adenosquamous carcinoma * Sarcomatoid carcinoma * Carcinoid tumor * Salivary gland-like carcinoma SCLC is generally considered to be the most aggressive of these major forms of lung cancer, with the worst long term prognosis and survival rates. As a result, it is recommended that all multiphasic malignant lung tumors (i.e. those with more than one histological pattern) that are found to contain any proportion of SCLC cells should be classified as c-SCLC, and not as<unk>  forms of any of the other histological variants present in the tumor. Currently, the only exception to this recommendation occurs in cases where anaplastic large cell lung carcinoma (LCLC) is the second histological component. In these instances, a minimum of 10% of the viable malignant cells present must be identified as LCLC before the tumor is considered to be a c-SCLC. Under the WHO-2004 classification scheme, c-SCLC is the only recognized variant of SCLC.
Combined small-cell lung carcinoma
Salivary gland–like carcinoma of the lung
Epithelial-myoepithelial carcinoma of the lung
Adenosquamous lung carcinoma
Large-cell lung carcinoma
Basaloid squamous cell lung carcinoma
Mucinous cystadenocarcinoma of the lung
Sarcomatoid carcinoma of the lung