SQUAMOUS CELL CARCINOMA OF THE LUNG Squamous cell carcinoma (SCC) is defined as a malignant epithelial tumor showing keratinization or intracellular bridges (or both) arising from bronchial epithelium. Previously, SCC, sometimes called epidermoid carcinoma, was the most common cell type, but that has changed in the past 1 or 2 decades in the United States, parts of Western Europe, and Japan. Currently, SCCs account for 20% of all lung cancers in the United States (http://seer.cancer.gov). The vast majority of SCC occurs in smokers. Recent Surveillance, Epidemiology and End Results (SEER) data report that SCC accounts for 24% of all cancers in men versus 16% in women. The recent decrease in SCC and increase in adenocarcinoma histology has been attributed to the change in the cigarette, from nonfilter to filter, and the decrease in tar. About 60% to 80% of these cancers arise centrally in mainstem, lobar, or segmental bronchi, but they may present as a peripheral lung lesion. SCC arises from the bronchial epithelium, and it is thought that the airway abnormality progresses through a series of changes from hyperplasia to dysplasia to carcinoma in situ, which is classified by World Health Organization as preinvasive and a precursor to SCC. Varying degrees of dysplasia have been associated with cumulative genetic alterations, but the critical genetic change(s) before developing frank cancer is still uncertain. Because of the tendency to occur centrally in the airway, SCC presents more commonly with hemoptysis, new or change in cough, chest pain, or pneumonia caused by bronchial obstruction. The usual radiographic presentation is a central mass or obstructing pneumonia with or without lobar collapse. About 10% to 20% of SCCs present as peripheral lesions. Cavitation may occur in 10% to 15% of all SCCs and is the most common histology associated with cavitation. The cavities are usually thick walled. Cavitation in the lung may also be caused by obstructive pneumonia and abscess formation. Sputum cytology has the highest diagnostic yield with this cell type because of the predominant central location. Bronchoscopy with brushings and biopsy are diagnostic in more than 90% of SCCs when the cancer is visible endoscopically. The yield for peripheral lesions that are endoscopically negative is significantly less and depends on the size of the tumor. For lesions smaller than 2 cm in diameter, transthoracic needle aspiration has the highest diagnostic yield if a tissue diagnosis is required before surgical resection. SCC in situ (pre invasive lesion) has an unpredictable course, and the treatment is a topic of current debate. Surgery is the treatment of choice for early-stage disease (stage I or II). Combination chemotherapy and radiotherapy are recommended for good performance score patients with unresectable stage III A or B disease. Stage IV (metastatic disease) is generally treated with systemic chemotherapy, but treatment is noncurative (palliative). It was previously believed that SCC was more slow-growing than other cell types, but recent analysis of a large international database that controlled for stage of disease does not demonstrate definite survival benefit of SCC versus other non–small cell histologies. In the past, SCCs have been treated the same as all other non–small cell histologies, but recent data show that optimal treatment depends on specific typing.