Large cell carcinoma is defined as an undifferentiated carcinoma without the characteristic features of squamous cell, small cell, or adeno-carcinomas. Diagnosis is largely based on exclusion of the other cell types of lung cancer by light microscopy. Large cell carcinoma grows rapidly and is usually quite large by the time it is diagnosed. Most of colony stimulating factor-producing lung cancers previously reported are large cell carcinomas. These colony stimulating factors are considered to contribute to the progressive nature of large cell carcinoma. The radiographic appearance of large cell carcinoma is often larger than 4 cm in diameter. The margins of the mass are poorly defined and lobulated while cavitation remains infrequent. Giant cell carcinoma, which is a variant of large cell carcinoma, is a particularly aggressive subtype with a poor prognosis. Metastases occur fairly late in the course of large cell carcinoma. The sites of metastases (brain, bone, adrenal glands, and liver) are similar to those involved with adenocarcinoma, although the gastrointestinal tract metastases are more commonly involved in large cell carcinoma.