Columnar ciliated cell metaplasia squamous cell carcinoma
Squamous cell carcinoma is highly associated with exposure to tobacco smoke and genetic aberrations, many of which are chromosome deletions involving tumor suppressor loci.
Squamous cell carcinoma is most commonly found in men and is strongly associated with smoking. Precursors lesions that give rise to invasive squamous cell carcinoma are well characterized. Squamous cell carcinomas are often antedated by squamous metaplasia or dysplasia in the bronchial epithelium, which then transforms to carcinoma in situ, a phase that may last for several years. By this time, atypical cells may be identified in cytologic smears of sputum or in bronchial lavage fluids or brushings, although the lesion is asymptomatic and undetectable on radiographs. Eventually, an invasive squamous cell carcinoma appears. The tumor may then follow a variety of paths. It may grow exophytically into the bronchial lumen, producing an intraluminal mass. With further enlargement the bronchus becomes obstructed, leading to distal atelectasis and infection. The tumor may also penetrate the wall of the bronchus and infiltrate along the peribronchial tissue into the adjacent carina or mediastinum. In other instances, the tumor grows along a broad front to produce a cauliflower-like intraparenchymal mass that pushes lung substance ahead of it. As in almost all types of lung cancer, the neoplastic tissue is gray-white and firm to hard. Especially when the tumors are bulky, focal areas of hemorrhage or necrosis may appear to produce red or yellowwhite mottling and softening. Sometimes these necrotic foci cavitate.
Histologically, squamous cell carcinoma is characterized by the presence of keratinization and/or intercellular bridges. Keratinization may take the form of squamous pearls or individual cells with markedly eosinophilic dense cytoplasm. These features are prominent in well-differentiated tumors, are easily seen but not extensive in moderately differentiated tumors, and are focally seen in poorly differentiated tumors. Mitotic activity is higher in poorly differentiated tumors. In the past, most squamous cell carcinomas were seen to arise centrally from the segmental or subsegmental bronchi. However, the incidence of squamous cell carcinoma of the peripheral lung is increasing. Squamous metaplasia, epithelial dysplasia, and foci of frank carcinoma in situ may be seen in bronchial epithelium adjacent to the tumor mass.