Giant-cell carcinoma of the lung (GCCL) is a rare histological form of large-cell lung carcinoma, a subtype of undifferentiatedlung cancer, traditionally classified within the non-small-cell lung carcinomas (NSCLC).
The characteristic feature of this highly lethal malignancy is the distinctive lightmicroscopic appearance of its extremely large cells, which are bizarre and highly pleomorphic, and which often contain more than one huge, misshapen, pleomorphic nucleus (“syncytia“), which result from cell fusion.
Although it is common in the lung cancer literature to refer to histologically mixed tumors containing significant numbers of malignant giant cells as “giant-cell carcinomas”, technically a diagnosis of “giant-cell carcinoma” should be limited strictly to neoplasms containing only malignant giant cells (i.e. “pure” giant-cell carcinoma).
Aside from the great heterogeneity seen in lung cancers (especially those occurring among tobacco smokers), the considerable variability in diagnostic and sampling techniques used in medical practice, the high relative proportion of individuals with suspected GCCL who do not undergo complete surgicalresection, and the near-universal lack of complete sectioning and pathological examination of resected tumor specimens prevent high levels of quantitative accuracy.
For several decades, primary lung cancers were consistently dichotomously classified for treatment and research purposes into small-cell lung carcinomas (SCLCs) and non-small-cell lung carcinomas (NSCLCs), based on an oversimplified approach that is now clearly outmoded. The new paradigm recognizes that lung cancers are a large and extremely heterogeneous family of malignant neoplasms, with over 50 different histological variants included in the 4th (2004) revision of the World Health Organization typing system, the most widely used lung cancer classification scheme (“WHO-2004”). These variants are increasingly appreciated as having different genetic, biological, and clinical properties, including prognoses and responses to treatment regimens, and therefore, that correct and consistent histological classification of lung cancers are necessary to validate and implement optimum management strategies.
About 1% of lung cancers are sarcomas, germ cell tumors, and hematopoietic tumors, while 99% of lung cancers are carcinoma. Carcinomas are tumors composed of transformed, abnormal cells with epithelial tissue architecture and/or molecular characteristics, and which derive from embryonicendoderm. Eight major taxa of lung carcinomas are recognized within the WHO-2004 classification:
- Small-cell carcinoma
- Squamous cell carcinoma
- Large-cell carcinoma
- Adenosquamous carcinoma
- Sarcomatoid carcinoma
- Salivary gland-like carcinoma
The subclassification of GCCL among these major taxa has undergone significant changes in recent decades. Under the 2nd revision (1981) of the WHO classification, it was considered a subtype of large-cell carcinoma. In the 3rd (1999) revision, it was placed within a taxon called “Carcinomas with Pleomorphic, Sarcomatoid, or Sarcomatous Elements”, along with pleomorphic carcinoma, spindle cell carcinoma, carcinosarcoma, and pulmonary blastoma, which are (arguably) related variants. While the 4th revision (“WHO-2004”) retained the same grouping of lesions as the 3rd revision, the name of the major taxon was shortened to “sarcomatoid carcinomas“.
The current rules for classifying lung cancers under WHO-2004, while useful and improved, remain to some extent fairly complex, ambiguous, arbitrary, and incomplete. Although it is fairly common for mixed tumors that are seen to contain malignant giant cells to be called “giant-cell carcinomas”, accurate classification of a pulmonary tumor as a GCCL requires that the entire tumor consists only of malignant giant cells. Therefore, complete sampling of the entire tumor — obtained via a surgicalresection — is absolutely necessary for a definitive diagnosis of GCCL to be made.