Even when a central mass is present, lobar collapse is uncommon because the tumor tends not to obstruct the bronchus. Both tissue and cytologic specimens are useful in diagnosing the disease. Once a histologic diagnosis of SCC of the lung is made, the extent of tumor spread is determined. If no metastatic sites outside the thorax are found, limited disease should be staged by the TNM system used for nonsmall cell carcinoma in order to diagnose the small number of patients who may benefit from surgical resection. In contrast to central carcinoid tumors that form polypoid masses in the bronchial lumen, small cell cancers often invade the wall directly, producing only a slight irregularity of the surface mucosa and no luminal stenosis, although obstructive tumors do occur.
Peripheral tumors appear as discrete nodules.
In either location, tumors are firm and grey-white with variable necrosis. Although no clinical significance of the classification has emerged, it is useful for 2 reasons. Fragile and easily crushed, cells from endobronchial biopsies often show smearing of nuclear material called crush artifact . Spindling of cells is common just as in carcinoid tumors. There may be scattered, multinucleated tumor giant cells.