SCLCs usually arise in central bronchi, but they may also occur peripherally. They tend to grow rapidly, invade and spread both early and widely. Invasion of adjacent structures is common. Pleural effusions may be caused by extension of the cancer to the pleural surface, by thoracic duct involvement in the mediastinum, or by obstruction of pulmonary lymphatics. Hoarseness or dysphagia may be secondary either to invasion of the left recurrent laryngeal nerve or to diaphragmatic paralysis from phrenic nerve involvement.
Lymphatic spread is similar to the behaviour of non-small cell lung cancer.
Other metastases, including those to the remaining lung tissue, opposite lung, pancreas, spleen, heart, thyroid, eye, ovary, kidneys, adrenals, soft tissue, and other internal organs, may be observed. The frequency of metastases rises during the course of the disease. Spinal, epidural or leptomeningeal space metastatic disease can be observed. 5.2.1 Extension of disease Limited-stage disease is by far the most important favorable prognostic factor. More recently supraclavicular lymphadenopathy and pleural effusions have been included in the limited-stage category, but if they are present, prognosis becomes worse.