Small cell lung cancer (SCLC), also known as oat cell lung cancer, is a subtype of bronchogenic carcinoma separated from non-small-cell lung cancer (NSCLC) as it has a unique presentation, imaging appearances, treatment, and prognosis. SCLCs are neuroendocrine tumors of the lung that rapidly grow, are highly malignant, widely metastasize, and, despite showing an initial response to chemotherapy and radiotherapy, 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 significantly vary and can present in the following ways:
- weight loss
- primary tumor
- local invasion
- metastatic spread (affecting ~70% of patients are presentation)
- paraneoplastic syndromes
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, usually arising adjacent to a lobar or main bronchus 3.
As previously mentioned, small-cell tumors are located centrally in the vast majority of cases. They arise from main-stem of lobar bronchi and thus appear as hilar or perihilar masses 2, and frequently have mediastinal lymph node involvement at the 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.
SCLCs are usually characterized as a mass lesion, where necrosis and hemorrhage are both common. Only rarely they present as a solitary pulmonary nodule.
For tumor staging, please refer to the article on IASLC (International Association for the Study of Lung Cancer) 8th edition lung cancer staging system (Since 2013, small cell lung cancer is staged the same way as non-small cell lung cancer).
Treatment and prognosis
Most cases will present in advanced stages, not operable, and with a dismal prognosis. Only about 5% of patients present at an early stage (Ia, Ib, or IIa), with a potentially curable disease. These patients are usually managed with an aggressive chemo-radiation therapy and, selected ones, with lobectomy associated with mediastinal lymph node dissection 4,5.
Surgical excision is commonly not recommended beyond these early stages, as studies have shown that any nodal involvement (N1–3 disease) will not benefit from the excisional treatment 4,5.
Brain metastases are found in up to a quarter of patients at presentation 4 and are known as a common site of disease recurrence after an initial treatment response. Prophylactic cerebral irradiation (PCI) can be offered for those with adequate systemic control and without metastases to the CNS 4.
Advanced disease (stage IV) is managed only with chemotherapy aiming for palliation and symptoms control.
Imaging differential considerations include:
- 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
- 4. Alvarado-Luna G, Morales-Espinosa D. Treatment for small cell lung cancer, where are we now?-a review. (2016) Translational lung cancer research. 5 (1): 26-38. doi:10.3978/j.issn.2218-6751.2016.01.13 - Pubmed
- 5. Schneider BJ, Saxena A, Downey RJ. Surgery for early-stage small cell lung cancer. (2011) Journal of the National Comprehensive Cancer Network : JNCCN. 9 (10): 1132-9. Pubmed