Small cell lung cancer
Small cell lung cancer (SCLC) (also known as oat cell lung cancer) is a sub type of bronchogenic carcinoma and considered separately from non small-cell lung cancer (NSCLC) as it has unique presentation, imaging appearances, treatment, and prognosis. Small cell lung cancers rapidly grow, are highly malignant, widely metastasize (60-80% at time of diagnosis) and show initial response to chemotherapy and radiotherapy. Despite this, SCLC's have a very poor prognosis and are usually unresectable.
Small cell lung cancers represent 15-20% of lung cancers 1 and is strongly associated with cigarette smoking.
Clinical presentation can significanctly vary and can present in the following ways.
- weight loss
- primary tumor
- local invasion
- metastatic spread
- bone pain (bone metastases)
- focal neurological deficit (CNS involvement)
- right upper quadrant pain (liver metastases)
- paraneoplastic syndromes (see bronchogenic carcinoma)
Small cell carcinoma is considered a neuroendocrine tumor of the lung. It arises from the bronchial mucosa. Local invasion occurs in the submucosa with subsequent invasion of peribronchial connective tissue. Cells are small, oval, with scant cytoplasm and a high mitotic count.
Approximately 90-95% of SCLCs occur centrally, and usually arising in a lobar or main bronchus 3.
Small cell cell tumors are located centrally in the vast majority of cases (90%). They arise from main-stem of lobar bronchi, and thus appear as hilar or perihilar masses 2. They frequently have mediastinal lymph node involvement at presentation.
Appearances on chest x-rays are non-specific. They may be seen as a hilar/perihilar mass usually with mediastinal widening due to lymph node enlargement 2. In fact, the mediastinal involvement is often the most striking feature and the primary mass may be inapparent.
On CT mediastinal involvement may appear similar to lymphoma, with numerous enlarged nodes. Direct infiltration of adjacent structures is more common. Small cell carcinoma of the lung is the most common cause of SVC obstruction, due to both compression/thrombosis and/or direct infiltration 2.
Necrosis and hemorrhage are both common. Only rarely do small cell carcinomas present as a solitary pulmonary nodule.
CT is able to stage small cell cell lung cancer.
Treatment and prognosis
Small cell lung cancer is rarely operable at the time of diagnosis. Initially the TNM system of staging was not used. It was traditionally divided using a two-stage system, i.e. limited and extensive (see small cell lung cancer staging).
Limited disease is treated using combined chemotherapy and radiotherapy with a 5 year survival rate 15-25%.
Extensive disease is treated with palliative chemotherapy and supportive care with a 2 year survival 20%.
Since 2013 small cell lung cancer is staged the same way as non small cell lung cancer.
Imaging imaging differential considerations include
- non small-cell lung cancer
- pulmonary sarcoma (rare)
- pulmonary metastases
- benign lung lesions