Small cell lung cancer
Small cell lung cancer (SCLC), also known as oat cell lung cancer, is a subtype of bronchogenic carcinoma and considered separate from non-small-cell lung cancer (NSCLC) as it has a unique presentation, imaging appearances, treatment, and prognosis. Small cell lung cancers rapidly grow, are highly malignant, widely metastasise and show an initial response to chemotherapy and radiotherapy. Despite this, SCLCs have a poor prognosis and are usually unresectable.
Small cell lung cancers represent 15-20% of lung cancers 1 and are strongly associated with cigarette smoking.
Clinical presentation can significanctly vary and can present in the following ways:
- weight loss
- primary tumour
- local invasion
- metastatic spread (affecting ~70% of patients are presentation)
- 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 tumour 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 tumours 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 haemorrhage are both common. Only rarely do small cell carcinomas present as a solitary pulmonary nodule.
CT is able to stage small 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 of ~20%. Extensive disease is treated with palliative chemotherapy and supportive care with a 2-year survival rate of 20%.
Since 2013 small cell lung cancer is staged the same way as non-small cell lung cancer.
Imaging differential considerations include:
- non-small-cell lung cancer
- pulmonary sarcoma (rare)
- pulmonary metastases
- benign lung lesions
lung cancer: overview
non small-cell lung cancer
- adenosquamous carcinoma
- large cell carcinoma
- primary sarcomatoid carcinoma of lung
- squamous cell carcinoma
- salivary gland type tumours
- pulmonary neuroendocrine tumours
- preinvasive lesions
- benign neoplasms
- pulmonary metastases
- lung cancer screening
- lung cancer staging
- non small-cell lung cancer
- 1. Shields TW, LoCicero J, Ponn RB. General thoracic surgery. Lippincott Williams & Wilkins. (2005) ISBN:078173889X. Read it at Google Books - Find it at Amazon
- 2. Collins J, Stern EJ. Chest radiology, the essentials. Lippincott Williams & Wilkins. (2007) ISBN:0781763142. Read it at Google Books - Find it at Amazon
- 3. Chong S, Lee KS, Chung MJ et-al. Neuroendocrine tumors of the lung: clinical, pathologic, and imaging findings. Radiographics. 2006;26 (1): 41-57. Radiographics (full text) - doi:10.1148/rg.261055057 - Pubmed citation