| Subtype | Characteristics |
| Classical SCLC | Small round, oval or spindle-shaped cells with scant cytoplasm, ill-defined borders, finely granular nuclear chromatin and absent or inconspicuous nucleoli. High mitotic count. Characteristic crush phenomena due to the soft texture of the tumour and mechanical alterations. Histomorphological grading G1 to G4 not applicable. |
| Typical/atypical carcinoid | Usually less aggressive tumour. |
| Large cell neuroendocrine tumour | Proliferation index relevant for classification. |
| Combined SCLC | Small-cell carcinoma with an additional component of any of the histological types of NSCLC |
WHO: World Health Organization; IASLC: International Association for the Study of Lung Cancer; SCLC: small cell lung cancer; NSCLC: non-small cell lung cancer.